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 $44.42   4.161%   $46.2683   $46.27   $46.25   $46.30  
  Purchase #2 $247.93   5.195%   $260.81   $260.81   $260.80   $260.80  
  Purchase #3 $83.65   6.587%   $89.16   $89.16   $89.15   $89.20  
  Purchase #4 $33.94   3.185%   $35.021   $35.02   $35.00   $35.00  
  Purchase #5 $83.32   9.310%   $91.0771   $91.08   $91.10   $91.10  
  Purchase #6 $199.35   13.429%   $226.1207   $226.12   $226.10   $226.10  
  Purchase #7 $98.98   5.804%   $104.7248   $104.72   $104.70   $104.70  
  7 purchase totals = $791.59       $853.1819   $853.18   $853.10   $853.20