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 $87.74   13.137%   $99.2664   $99.27   $99.25   $99.30  
  Purchase #2 $172.97   13.606%   $196.5043   $196.50   $196.50   $196.50  
  Purchase #3 $12.95   7.632%   $13.9383   $13.94   $13.95   $13.90  
  Purchase #4 $108.80   12.131%   $121.9985   $122.00   $122.00   $122.00  
  Purchase #5 $16.65   10.600%   $18.4149   $18.41   $18.40   $18.40  
  Purchase #6 $202.88   10.828%   $224.8478   $224.85   $224.85   $224.80  
  Purchase #7 $213.70   8.329%   $231.4991   $231.50   $231.50   $231.50  
  7 purchase totals = $815.69       $906.4693   $906.47   $906.45   $906.40