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 $63.65   4.513%   $66.5225   $66.52   $66.50   $66.50  
  Purchase #2 $115.71   3.859%   $120.1752   $120.18   $120.20   $120.20  
  Purchase #3 $157.91   5.105%   $165.9713   $165.97   $165.95   $166.00  
  Purchase #4 $102.73   3.666%   $106.4961   $106.50   $106.50   $106.50  
  Purchase #5 $150.57   5.319%   $158.5788   $158.58   $158.60   $158.60  
  Purchase #6 $52.74   9.194%   $57.5889   $57.59   $57.60   $57.60  
  Purchase #7 $239.66   9.360%   $262.0922   $262.09   $262.10   $262.10  
  7 purchase totals = $882.97       $937.4250   $937.43   $937.45   $937.50