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 $217.99   9.176%   $237.9928   $237.99   $238.00   $238.00  
  Purchase #2 $73.56   4.587%   $76.9342   $76.93   $76.95   $76.90  
  Purchase #3 $29.48   4.176%   $30.7111   $30.71   $30.70   $30.70  
  Purchase #4 $240.77   11.227%   $267.8012   $267.80   $267.80   $267.80  
  Purchase #5 $85.93   11.575%   $95.8764   $95.88   $95.90   $95.90  
  Purchase #6 $48.33   9.254%   $52.8025   $52.80   $52.80   $52.80  
  Purchase #7 $238.45   5.197%   $250.8422   $250.84   $250.85   $250.80  
  7 purchase totals = $934.51       $1,012.9604   $1,012.95   $1,013.00   $1,012.90