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 $68.35   10.681%   $75.6505   $75.65   $75.65   $75.70  
  Purchase #2 $151.78   5.544%   $160.1947   $160.19   $160.20   $160.20  
  Purchase #3 $99.74   13.314%   $113.0194   $113.02   $113.00   $113.00  
  Purchase #4 $40.76   12.737%   $45.9516   $45.95   $45.95   $46.00  
  Purchase #5 $91.29   10.732%   $101.0872   $101.09   $101.10   $101.10  
  Purchase #6 $172.73   5.520%   $182.2647   $182.26   $182.25   $182.30  
  Purchase #7 $94.93   12.847%   $107.1257   $107.13   $107.15   $107.10  
  7 purchase totals = $719.58       $785.2938   $785.29   $785.30   $785.40