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 $228.43   8.717%   $248.3422   $248.34   $248.35   $248.30  
  Purchase #2 $211.67   13.660%   $240.5841   $240.58   $240.60   $240.60  
  Purchase #3 $107.40   11.164%   $119.3901   $119.39   $119.40   $119.40  
  Purchase #4 $171.97   11.124%   $191.0999   $191.10   $191.10   $191.10  
  Purchase #5 $161.90   5.215%   $170.3431   $170.34   $170.35   $170.30  
  Purchase #6 $210.48   9.283%   $230.0189   $230.02   $230.00   $230.00  
  Purchase #7 $148.74   5.775%   $157.3297   $157.33   $157.35   $157.30  
  7 purchase totals = $1,240.59       $1,357.1080   $1,357.10   $1,357.15   $1,357.00