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 $62.72   8.607%   $68.1183   $68.12   $68.10   $68.10  
  Purchase #2 $213.51   10.685%   $236.3235   $236.32   $236.30   $236.30  
  Purchase #3 $235.67   4.563%   $246.4236   $246.42   $246.40   $246.40  
  Purchase #4 $143.29   6.548%   $152.6726   $152.67   $152.65   $152.70  
  Purchase #5 $95.25   3.298%   $98.3913   $98.39   $98.40   $98.40  
  Purchase #6 $58.74   4.624%   $61.4561   $61.46   $61.45   $61.50  
  Purchase #7 $170.42   6.867%   $182.1227   $182.12   $182.10   $182.10  
  7 purchase totals = $979.60       $1,045.5081   $1,045.50   $1,045.40   $1,045.50