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 $238.97   10.854%   $264.9078   $264.91   $264.90   $264.90  
  Purchase #2 $44.93   12.279%   $50.447   $50.45   $50.45   $50.40  
  Purchase #3 $218.49   8.752%   $237.6122   $237.61   $237.60   $237.60  
  Purchase #4 $59.83   12.615%   $67.3776   $67.38   $67.40   $67.40  
  Purchase #5 $179.38   8.576%   $194.7636   $194.76   $194.75   $194.80  
  Purchase #6 $51.70   13.632%   $58.7477   $58.75   $58.75   $58.70  
  Purchase #7 $140.69   3.199%   $145.1907   $145.19   $145.20   $145.20  
  7 purchase totals = $933.99       $1,019.0466   $1,019.05   $1,019.05   $1,019.00