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 $44.39   8.236%   $48.046   $48.05   $48.05   $48.00  
  Purchase #2 $90.34   3.145%   $93.1812   $93.18   $93.20   $93.20  
  Purchase #3 $203.90   4.828%   $213.7443   $213.74   $213.75   $213.70  
  Purchase #4 $139.29   13.504%   $158.0997   $158.10   $158.10   $158.10  
  Purchase #5 $23.70   6.212%   $25.1722   $25.17   $25.15   $25.20  
  Purchase #6 $18.53   9.418%   $20.2752   $20.28   $20.30   $20.30  
  Purchase #7 $205.64   10.189%   $226.5927   $226.59   $226.60   $226.60  
  7 purchase totals = $725.79       $785.1113   $785.11   $785.15   $785.10