Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $210.75   13.278%   $238.7334   $238.73   $238.75   $238.70  
  Purchase #2 $97.28   6.245%   $103.3551   $103.36   $103.35   $103.40  
  Purchase #3 $91.71   13.578%   $104.1624   $104.16   $104.15   $104.20  
  Purchase #4 $187.53   11.607%   $209.2966   $209.30   $209.30   $209.30  
  Purchase #5 $201.49   9.427%   $220.4845   $220.48   $220.50   $220.50  
  Purchase #6 $204.39   10.224%   $225.2868   $225.29   $225.30   $225.30  
  Purchase #7 $204.63   13.294%   $231.8335   $231.83   $231.85   $231.80  
  7 purchase totals = $1,197.78       $1,333.1523   $1,333.15   $1,333.20   $1,333.20