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 $42.95   12.728%   $48.4167   $48.42   $48.40   $48.40  
  Purchase #2 $76.51   8.255%   $82.8259   $82.83   $82.85   $82.80  
  Purchase #3 $118.66   9.251%   $129.6372   $129.64   $129.65   $129.60  
  Purchase #4 $126.57   5.468%   $133.4908   $133.49   $133.50   $133.50  
  Purchase #5 $165.91   6.759%   $177.1239   $177.12   $177.10   $177.10  
  Purchase #6 $161.28   6.521%   $171.7971   $171.80   $171.80   $171.80  
  Purchase #7 $206.78   4.853%   $216.815   $216.82   $216.80   $216.80  
  7 purchase totals = $898.66       $960.1066   $960.12   $960.10   $960.00