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 $241.53   9.611%   $264.7434   $264.74   $264.75   $264.70  
  Purchase #2 $20.40   8.811%   $22.1974   $22.20   $22.20   $22.20  
  Purchase #3 $29.28   10.265%   $32.2856   $32.29   $32.30   $32.30  
  Purchase #4 $244.76   4.310%   $255.3092   $255.31   $255.30   $255.30  
  Purchase #5 $66.85   7.659%   $71.97   $71.97   $71.95   $72.00  
  Purchase #6 $11.35   4.496%   $11.8603   $11.86   $11.85   $11.90  
  Purchase #7 $244.60   6.140%   $259.6184   $259.62   $259.60   $259.60  
  7 purchase totals = $858.77       $917.9843   $917.99   $917.95   $918.00