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 $109.55   13.158%   $123.9646   $123.96   $123.95   $124.00  
  Purchase #2 $226.90   7.487%   $243.888   $243.89   $243.90   $243.90  
  Purchase #3 $66.60   9.814%   $73.1361   $73.14   $73.15   $73.10  
  Purchase #4 $61.74   8.700%   $67.1114   $67.11   $67.10   $67.10  
  Purchase #5 $154.58   13.700%   $175.7575   $175.76   $175.75   $175.80  
  Purchase #6 $14.60   5.373%   $15.3845   $15.38   $15.40   $15.40  
  Purchase #7 $127.43   6.243%   $135.3855   $135.39   $135.40   $135.40  
  7 purchase totals = $761.40       $834.6276   $834.63   $834.65   $834.70