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 $36.71   11.276%   $40.8494   $40.85   $40.85   $40.80  
  Purchase #2 $182.40   8.122%   $197.2145   $197.21   $197.20   $197.20  
  Purchase #3 $126.62   6.150%   $134.4071   $134.41   $134.40   $134.40  
  Purchase #4 $194.64   6.622%   $207.5291   $207.53   $207.55   $207.50  
  Purchase #5 $163.46   13.410%   $185.38   $185.38   $185.40   $185.40  
  Purchase #6 $10.69   9.612%   $11.7175   $11.72   $11.70   $11.70  
  Purchase #7 $229.27   7.468%   $246.3919   $246.39   $246.40   $246.40  
  7 purchase totals = $943.79       $1,023.4895   $1,023.49   $1,023.50   $1,023.40