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 $65.91   11.828%   $73.7058   $73.71   $73.70   $73.70  
  Purchase #2 $161.26   13.329%   $182.7543   $182.75   $182.75   $182.80  
  Purchase #3 $198.57   6.208%   $210.8972   $210.90   $210.90   $210.90  
  Purchase #4 $104.64   6.181%   $111.1078   $111.11   $111.10   $111.10  
  Purchase #5 $106.72   3.481%   $110.4349   $110.43   $110.45   $110.40  
  Purchase #6 $200.73   5.769%   $212.3101   $212.31   $212.30   $212.30  
  Purchase #7 $144.45   9.828%   $158.6465   $158.65   $158.65   $158.60  
  7 purchase totals = $982.28       $1,059.8566   $1,059.86   $1,059.85   $1,059.80