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 $166.98   12.341%   $187.587   $187.59   $187.60   $187.60  
  Purchase #2 $72.61   5.686%   $76.7386   $76.74   $76.75   $76.70  
  Purchase #3 $170.42   5.272%   $179.4045   $179.40   $179.40   $179.40  
  Purchase #4 $46.87   7.448%   $50.3609   $50.36   $50.35   $50.40  
  Purchase #5 $250.38   6.545%   $266.7674   $266.77   $266.75   $266.80  
  Purchase #6 $157.51   6.523%   $167.7844   $167.78   $167.80   $167.80  
  Purchase #7 $163.78   10.421%   $180.8475   $180.85   $180.85   $180.80  
  7 purchase totals = $1,028.55       $1,109.4903   $1,109.49   $1,109.50   $1,109.50