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 $55.44   12.671%   $62.4648   $62.46   $62.45   $62.50  
  Purchase #2 $236.42   3.182%   $243.9429   $243.94   $243.95   $243.90  
  Purchase #3 $110.42   6.777%   $117.9032   $117.90   $117.90   $117.90  
  Purchase #4 $114.52   6.242%   $121.6683   $121.67   $121.65   $121.70  
  Purchase #5 $60.28   11.323%   $67.1055   $67.11   $67.10   $67.10  
  Purchase #6 $169.48   3.401%   $175.244   $175.24   $175.25   $175.20  
  Purchase #7 $12.53   4.694%   $13.1182   $13.12   $13.10   $13.10  
  7 purchase totals = $759.09       $801.4469   $801.44   $801.40   $801.40