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 $234.47   3.756%   $243.2767   $243.28   $243.30   $243.30  
  Purchase #2 $205.29   10.517%   $226.8803   $226.88   $226.90   $226.90  
  Purchase #3 $41.52   3.577%   $43.0052   $43.01   $43.00   $43.00  
  Purchase #4 $57.47   12.638%   $64.7331   $64.73   $64.75   $64.70  
  Purchase #5 $219.55   7.517%   $236.0536   $236.05   $236.05   $236.10  
  Purchase #6 $51.78   12.541%   $58.2737   $58.27   $58.25   $58.30  
  Purchase #7 $142.94   12.761%   $161.1806   $161.18   $161.20   $161.20  
  7 purchase totals = $953.02       $1,033.4032   $1,033.40   $1,033.45   $1,033.50