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 $107.72   8.288%   $116.6478   $116.65   $116.65   $116.60  
  Purchase #2 $91.46   11.462%   $101.9431   $101.94   $101.95   $101.90  
  Purchase #3 $244.74   3.236%   $252.6598   $252.66   $252.65   $252.70  
  Purchase #4 $110.93   10.857%   $122.9737   $122.97   $122.95   $123.00  
  Purchase #5 $30.43   7.849%   $32.8185   $32.82   $32.80   $32.80  
  Purchase #6 $121.64   10.451%   $134.3526   $134.35   $134.35   $134.40  
  Purchase #7 $159.77   4.622%   $167.1546   $167.15   $167.15   $167.20  
  7 purchase totals = $866.69       $928.5501   $928.54   $928.50   $928.60