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 $240.97   8.195%   $260.7175   $260.72   $260.70   $260.70  
  Purchase #2 $88.95   5.709%   $94.0282   $94.03   $94.05   $94.00  
  Purchase #3 $59.50   10.169%   $65.5506   $65.55   $65.55   $65.60  
  Purchase #4 $188.40   3.699%   $195.3689   $195.37   $195.35   $195.40  
  Purchase #5 $87.75   6.283%   $93.2633   $93.26   $93.25   $93.30  
  Purchase #6 $190.67   6.444%   $202.9568   $202.96   $202.95   $203.00  
  Purchase #7 $125.49   11.854%   $140.3656   $140.37   $140.35   $140.40  
  7 purchase totals = $981.73       $1,052.2509   $1,052.26   $1,052.20   $1,052.40