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 $86.61   11.112%   $96.2341   $96.23   $96.25   $96.20  
  Purchase #2 $173.83   9.536%   $190.4064   $190.41   $190.40   $190.40  
  Purchase #3 $102.53   5.232%   $107.8944   $107.89   $107.90   $107.90  
  Purchase #4 $147.43   10.743%   $163.2684   $163.27   $163.25   $163.30  
  Purchase #5 $170.64   11.105%   $189.5896   $189.59   $189.60   $189.60  
  Purchase #6 $38.64   13.340%   $43.7946   $43.79   $43.80   $43.80  
  Purchase #7 $167.46   12.600%   $188.56   $188.56   $188.55   $188.60  
  7 purchase totals = $887.14       $979.7475   $979.74   $979.75   $979.80