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 $182.33   10.593%   $201.6442   $201.64   $201.65   $201.60  
  Purchase #2 $117.29   10.239%   $129.2993   $129.30   $129.30   $129.30  
  Purchase #3 $169.93   8.644%   $184.6187   $184.62   $184.60   $184.60  
  Purchase #4 $54.38   3.814%   $56.4541   $56.45   $56.45   $56.50  
  Purchase #5 $191.91   11.797%   $214.5496   $214.55   $214.55   $214.50  
  Purchase #6 $103.67   10.309%   $114.3573   $114.36   $114.35   $114.40  
  Purchase #7 $65.31   10.707%   $72.3027   $72.30   $72.30   $72.30  
  7 purchase totals = $884.82       $973.2259   $973.22   $973.20   $973.20