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 $111.90   9.331%   $122.3414   $122.34   $122.35   $122.30  
  Purchase #2 $207.59   4.829%   $217.6145   $217.61   $217.60   $217.60  
  Purchase #3 $42.32   8.715%   $46.0082   $46.01   $46.00   $46.00  
  Purchase #4 $92.29   5.611%   $97.4684   $97.47   $97.45   $97.50  
  Purchase #5 $199.81   5.285%   $210.37   $210.37   $210.35   $210.40  
  Purchase #6 $155.59   8.284%   $168.4791   $168.48   $168.50   $168.50  
  Purchase #7 $153.64   3.831%   $159.5259   $159.53   $159.55   $159.50  
  7 purchase totals = $963.14       $1,021.8075   $1,021.81   $1,021.80   $1,021.80