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 $219.86   12.682%   $247.7426   $247.74   $247.75   $247.70  
  Purchase #2 $57.88   4.232%   $60.3295   $60.33   $60.35   $60.30  
  Purchase #3 $179.91   13.658%   $204.4821   $204.48   $204.50   $204.50  
  Purchase #4 $151.45   13.707%   $172.2093   $172.21   $172.20   $172.20  
  Purchase #5 $126.68   3.815%   $131.5128   $131.51   $131.50   $131.50  
  Purchase #6 $210.58   3.182%   $217.2807   $217.28   $217.30   $217.30  
  Purchase #7 $19.44   6.473%   $20.6984   $20.70   $20.70   $20.70  
  7 purchase totals = $965.80       $1,054.2554   $1,054.25   $1,054.30   $1,054.20