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 $20.70   9.848%   $22.7385   $22.74   $22.75   $22.70  
  Purchase #2 $20.54   3.103%   $21.1774   $21.18   $21.20   $21.20  
  Purchase #3 $9.86   8.301%   $10.6785   $10.68   $10.70   $10.70  
  Purchase #4 $29.44   3.452%   $30.4563   $30.46   $30.45   $30.50  
  Purchase #5 $132.85   9.226%   $145.1067   $145.11   $145.10   $145.10  
  Purchase #6 $96.75   11.497%   $107.8733   $107.87   $107.85   $107.90  
  Purchase #7 $98.80   5.275%   $104.0117   $104.01   $104.00   $104.00  
  7 purchase totals = $408.94       $442.0424   $442.05   $442.05   $442.10