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 $19.47   11.555%   $21.7198   $21.72   $21.70   $21.70  
  Purchase #2 $32.42   12.239%   $36.3879   $36.39   $36.40   $36.40  
  Purchase #3 $15.44   3.418%   $15.9677   $15.97   $15.95   $16.00  
  Purchase #4 $206.60   7.872%   $222.8636   $222.86   $222.85   $222.90  
  Purchase #5 $143.45   12.820%   $161.8403   $161.84   $161.85   $161.80  
  Purchase #6 $117.99   6.203%   $125.3089   $125.31   $125.30   $125.30  
  Purchase #7 $104.97   8.384%   $113.7707   $113.77   $113.75   $113.80  
  7 purchase totals = $640.34       $697.8589   $697.86   $697.80   $697.90