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 $201.43   9.518%   $220.6021   $220.60   $220.60   $220.60  
  Purchase #2 $118.97   12.560%   $133.9126   $133.91   $133.90   $133.90  
  Purchase #3 $156.91   8.329%   $169.979   $169.98   $170.00   $170.00  
  Purchase #4 $242.90   8.560%   $263.6922   $263.69   $263.70   $263.70  
  Purchase #5 $222.47   9.396%   $243.3733   $243.37   $243.35   $243.40  
  Purchase #6 $92.39   6.659%   $98.5423   $98.54   $98.55   $98.50  
  Purchase #7 $84.94   9.823%   $93.2837   $93.28   $93.30   $93.30  
  7 purchase totals = $1,120.01       $1,223.3852   $1,223.37   $1,223.40   $1,223.40