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 $180.38   12.551%   $203.0195   $203.02   $203.00   $203.00  
  Purchase #2 $51.99   3.468%   $53.793   $53.79   $53.80   $53.80  
  Purchase #3 $222.48   7.344%   $238.8189   $238.82   $238.80   $238.80  
  Purchase #4 $195.80   11.538%   $218.3914   $218.39   $218.40   $218.40  
  Purchase #5 $51.45   5.734%   $54.4001   $54.40   $54.40   $54.40  
  Purchase #6 $157.72   8.754%   $171.5268   $171.53   $171.55   $171.50  
  Purchase #7 $18.40   10.170%   $20.2713   $20.27   $20.25   $20.30  
  7 purchase totals = $878.22       $960.2210   $960.22   $960.20   $960.20