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 $175.58   12.602%   $197.7066   $197.71   $197.70   $197.70  
  Purchase #2 $153.73   13.658%   $174.7264   $174.73   $174.75   $174.70  
  Purchase #3 $50.63   5.713%   $53.5225   $53.52   $53.50   $53.50  
  Purchase #4 $236.55   4.575%   $247.3722   $247.37   $247.35   $247.40  
  Purchase #5 $86.37   9.589%   $94.652   $94.65   $94.65   $94.70  
  Purchase #6 $40.43   11.356%   $45.0212   $45.02   $45.00   $45.00  
  Purchase #7 $18.42   10.311%   $20.3193   $20.32   $20.30   $20.30  
  7 purchase totals = $761.71       $833.3202   $833.32   $833.25   $833.30