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 $48.88   9.867%   $53.703   $53.70   $53.70   $53.70  
  Purchase #2 $81.73   8.312%   $88.5234   $88.52   $88.50   $88.50  
  Purchase #3 $24.84   4.773%   $26.0256   $26.03   $26.05   $26.00  
  Purchase #4 $61.71   12.815%   $69.6181   $69.62   $69.60   $69.60  
  Purchase #5 $59.85   10.584%   $66.1845   $66.18   $66.20   $66.20  
  Purchase #6 $220.47   7.697%   $237.4396   $237.44   $237.45   $237.40  
  Purchase #7 $60.53   3.357%   $62.562   $62.56   $62.55   $62.60  
  7 purchase totals = $558.01       $604.0562   $604.05   $604.05   $604.00