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 $217.82   8.556%   $236.4567   $236.46   $236.45   $236.50  
  Purchase #2 $39.79   10.323%   $43.8975   $43.90   $43.90   $43.90  
  Purchase #3 $169.59   11.672%   $189.3845   $189.38   $189.40   $189.40  
  Purchase #4 $23.54   8.443%   $25.5275   $25.53   $25.55   $25.50  
  Purchase #5 $77.77   11.431%   $86.6599   $86.66   $86.65   $86.70  
  Purchase #6 $190.32   7.798%   $205.1612   $205.16   $205.15   $205.20  
  Purchase #7 $169.30   5.515%   $178.6369   $178.64   $178.65   $178.60  
  7 purchase totals = $888.13       $965.7242   $965.73   $965.75   $965.80