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 $53.27   9.592%   $58.3797   $58.38   $58.40   $58.40  
  Purchase #2 $61.84   9.866%   $67.9411   $67.94   $67.95   $67.90  
  Purchase #3 $30.52   13.160%   $34.5364   $34.54   $34.55   $34.50  
  Purchase #4 $205.63   10.243%   $226.6927   $226.69   $226.70   $226.70  
  Purchase #5 $105.31   3.117%   $108.5925   $108.59   $108.60   $108.60  
  Purchase #6 $96.26   4.441%   $100.5349   $100.53   $100.55   $100.50  
  Purchase #7 $148.96   4.580%   $155.7824   $155.78   $155.80   $155.80  
  7 purchase totals = $701.79       $752.4597   $752.45   $752.55   $752.40