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 $237.80   11.216%   $264.4716   $264.47   $264.45   $264.50  
  Purchase #2 $119.55   3.647%   $123.91   $123.91   $123.90   $123.90  
  Purchase #3 $140.49   8.856%   $152.9318   $152.93   $152.95   $152.90  
  Purchase #4 $79.59   10.504%   $87.9501   $87.95   $87.95   $88.00  
  Purchase #5 $140.31   12.811%   $158.2851   $158.29   $158.30   $158.30  
  Purchase #6 $68.57   10.454%   $75.7383   $75.74   $75.75   $75.70  
  Purchase #7 $92.38   4.689%   $96.7117   $96.71   $96.70   $96.70  
  7 purchase totals = $878.69       $959.9986   $960.00   $960.00   $960.00