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 $59.39   3.670%   $61.5696   $61.57   $61.55   $61.60  
  Purchase #2 $50.92   3.256%   $52.578   $52.58   $52.60   $52.60  
  Purchase #3 $49.71   5.304%   $52.3466   $52.35   $52.35   $52.30  
  Purchase #4 $27.74   5.549%   $29.2793   $29.28   $29.30   $29.30  
  Purchase #5 $149.97   5.481%   $158.1899   $158.19   $158.20   $158.20  
  Purchase #6 $220.90   6.558%   $235.3866   $235.39   $235.40   $235.40  
  Purchase #7 $57.55   11.448%   $64.1383   $64.14   $64.15   $64.10  
  7 purchase totals = $616.18       $653.4883   $653.50   $653.55   $653.50