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 $56.50   4.790%   $59.2064   $59.21   $59.20   $59.20  
  Purchase #2 $220.67   7.244%   $236.6553   $236.66   $236.65   $236.70  
  Purchase #3 $59.95   12.479%   $67.4312   $67.43   $67.45   $67.40  
  Purchase #4 $68.95   5.429%   $72.6933   $72.69   $72.70   $72.70  
  Purchase #5 $55.56   13.794%   $63.2239   $63.22   $63.20   $63.20  
  Purchase #6 $218.37   11.717%   $243.9564   $243.96   $243.95   $244.00  
  Purchase #7 $147.94   6.843%   $158.0635   $158.06   $158.05   $158.10  
  7 purchase totals = $827.94       $901.2300   $901.23   $901.20   $901.30