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 $14.87   4.854%   $15.5918   $15.59   $15.60   $15.60  
  Purchase #2 $229.26   6.121%   $243.293   $243.29   $243.30   $243.30  
  Purchase #3 $65.71   6.355%   $69.8859   $69.89   $69.90   $69.90  
  Purchase #4 $53.78   13.304%   $60.9349   $60.93   $60.95   $60.90  
  Purchase #5 $204.30   4.543%   $213.5813   $213.58   $213.60   $213.60  
  Purchase #6 $89.42   7.347%   $95.9897   $95.99   $96.00   $96.00  
  Purchase #7 $195.50   3.349%   $202.0473   $202.05   $202.05   $202.00  
  7 purchase totals = $852.84       $901.3239   $901.32   $901.40   $901.30