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 $50.69   12.116%   $56.8316   $56.83   $56.85   $56.80  
  Purchase #2 $126.42   10.351%   $139.5057   $139.51   $139.50   $139.50  
  Purchase #3 $110.29   8.193%   $119.3261   $119.33   $119.35   $119.30  
  Purchase #4 $95.82   6.714%   $102.2534   $102.25   $102.25   $102.30  
  Purchase #5 $241.58   12.387%   $271.5045   $271.50   $271.50   $271.50  
  Purchase #6 $246.26   9.423%   $269.4651   $269.47   $269.45   $269.50  
  Purchase #7 $222.49   9.408%   $243.4219   $243.42   $243.40   $243.40  
  7 purchase totals = $1,093.55       $1,202.3083   $1,202.31   $1,202.30   $1,202.30