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 $54.31   10.506%   $60.0158   $60.02   $60.00   $60.00  
  Purchase #2 $22.76   13.136%   $25.7498   $25.75   $25.75   $25.70  
  Purchase #3 $214.82   3.168%   $221.6255   $221.63   $221.65   $221.60  
  Purchase #4 $124.87   7.195%   $133.8544   $133.85   $133.85   $133.90  
  Purchase #5 $210.28   11.350%   $234.1468   $234.15   $234.15   $234.10  
  Purchase #6 $159.45   11.255%   $177.3961   $177.40   $177.40   $177.40  
  Purchase #7 $49.87   11.143%   $55.427   $55.43   $55.45   $55.40  
  7 purchase totals = $836.36       $908.2154   $908.23   $908.25   $908.10