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 $191.56   7.826%   $206.5515   $206.55   $206.55   $206.60  
  Purchase #2 $66.29   8.544%   $71.9538   $71.95   $71.95   $72.00  
  Purchase #3 $69.27   11.480%   $77.2222   $77.22   $77.20   $77.20  
  Purchase #4 $23.92   5.251%   $25.176   $25.18   $25.20   $25.20  
  Purchase #5 $58.91   13.608%   $66.9265   $66.93   $66.95   $66.90  
  Purchase #6 $169.87   12.366%   $190.8761   $190.88   $190.90   $190.90  
  Purchase #7 $44.87   13.633%   $50.9871   $50.99   $51.00   $51.00  
  7 purchase totals = $624.69       $689.6932   $689.70   $689.75   $689.80