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 $214.38   13.490%   $243.2999   $243.30   $243.30   $243.30  
  Purchase #2 $117.31   11.784%   $131.1338   $131.13   $131.15   $131.10  
  Purchase #3 $114.78   4.206%   $119.6076   $119.61   $119.60   $119.60  
  Purchase #4 $204.33   13.805%   $232.5378   $232.54   $232.55   $232.50  
  Purchase #5 $7.73   9.616%   $8.4733   $8.47   $8.45   $8.50  
  Purchase #6 $137.56   12.694%   $155.0219   $155.02   $155.00   $155.00  
  Purchase #7 $58.47   13.317%   $66.2564   $66.26   $66.25   $66.30  
  7 purchase totals = $854.56       $956.3307   $956.33   $956.30   $956.30