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 $241.43   8.632%   $262.2702   $262.27   $262.25   $262.30  
  Purchase #2 $138.60   11.104%   $153.9901   $153.99   $154.00   $154.00  
  Purchase #3 $114.31   8.640%   $124.1864   $124.19   $124.20   $124.20  
  Purchase #4 $66.38   13.262%   $75.1833   $75.18   $75.20   $75.20  
  Purchase #5 $141.28   8.346%   $153.0712   $153.07   $153.05   $153.10  
  Purchase #6 $90.34   3.292%   $93.314   $93.31   $93.30   $93.30  
  Purchase #7 $87.40   10.124%   $96.2484   $96.25   $96.25   $96.20  
  7 purchase totals = $879.74       $958.2636   $958.26   $958.25   $958.30