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 $66.97   12.237%   $75.1651   $75.17   $75.15   $75.20  
  Purchase #2 $143.59   9.138%   $156.7113   $156.71   $156.70   $156.70  
  Purchase #3 $38.34   9.862%   $42.1211   $42.12   $42.10   $42.10  
  Purchase #4 $170.79   8.506%   $185.3174   $185.32   $185.30   $185.30  
  Purchase #5 $91.60   12.619%   $103.159   $103.16   $103.15   $103.20  
  Purchase #6 $192.27   11.310%   $214.0157   $214.02   $214.00   $214.00  
  Purchase #7 $114.69   3.525%   $118.7328   $118.73   $118.75   $118.70  
  7 purchase totals = $818.25       $895.2224   $895.23   $895.15   $895.20