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 $96.39   10.791%   $106.7914   $106.79   $106.80   $106.80  
  Purchase #2 $64.41   8.507%   $69.8894   $69.89   $69.90   $69.90  
  Purchase #3 $163.60   9.358%   $178.9097   $178.91   $178.90   $178.90  
  Purchase #4 $67.97   7.138%   $72.8217   $72.82   $72.80   $72.80  
  Purchase #5 $116.35   13.210%   $131.7198   $131.72   $131.70   $131.70  
  Purchase #6 $48.54   6.383%   $51.6383   $51.64   $51.65   $51.60  
  Purchase #7 $166.69   9.543%   $182.5972   $182.60   $182.60   $182.60  
  7 purchase totals = $723.95       $794.3675   $794.37   $794.35   $794.30