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 $64.71   3.517%   $66.9859   $66.99   $67.00   $67.00  
  Purchase #2 $210.48   6.358%   $223.8623   $223.86   $223.85   $223.90  
  Purchase #3 $243.94   5.239%   $256.72   $256.72   $256.70   $256.70  
  Purchase #4 $102.45   5.265%   $107.844   $107.84   $107.85   $107.80  
  Purchase #5 $82.49   6.476%   $87.8321   $87.83   $87.85   $87.80  
  Purchase #6 $41.96   8.521%   $45.5354   $45.54   $45.55   $45.50  
  Purchase #7 $158.98   5.126%   $167.1293   $167.13   $167.15   $167.10  
  7 purchase totals = $905.01       $955.9090   $955.91   $955.95   $955.80