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 $197.34   13.179%   $223.3474   $223.35   $223.35   $223.30  
  Purchase #2 $191.91   4.583%   $200.7052   $200.71   $200.70   $200.70  
  Purchase #3 $239.80   11.375%   $267.0773   $267.08   $267.10   $267.10  
  Purchase #4 $148.50   6.737%   $158.5044   $158.50   $158.50   $158.50  
  Purchase #5 $10.78   4.421%   $11.2566   $11.26   $11.25   $11.30  
  Purchase #6 $98.94   5.619%   $104.4994   $104.50   $104.50   $104.50  
  Purchase #7 $236.78   10.621%   $261.9284   $261.93   $261.95   $261.90  
  7 purchase totals = $1,124.05       $1,227.3187   $1,227.33   $1,227.35   $1,227.30