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 $22.84   10.537%   $25.2467   $25.25   $25.25   $25.20  
  Purchase #2 $191.36   7.106%   $204.958   $204.96   $204.95   $205.00  
  Purchase #3 $68.61   10.122%   $75.5547   $75.55   $75.55   $75.60  
  Purchase #4 $56.56   11.378%   $62.9954   $63.00   $63.00   $63.00  
  Purchase #5 $236.34   9.443%   $258.6576   $258.66   $258.65   $258.70  
  Purchase #6 $227.82   4.390%   $237.8213   $237.82   $237.80   $237.80  
  Purchase #7 $174.25   9.316%   $190.4831   $190.48   $190.50   $190.50  
  7 purchase totals = $977.78       $1,055.7168   $1,055.72   $1,055.70   $1,055.80