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 $214.91   9.277%   $234.8472   $234.85   $234.85   $234.80  
  Purchase #2 $58.86   9.303%   $64.3357   $64.34   $64.35   $64.30  
  Purchase #3 $94.59   13.142%   $107.021   $107.02   $107.00   $107.00  
  Purchase #4 $180.47   8.252%   $195.3624   $195.36   $195.35   $195.40  
  Purchase #5 $31.30   8.727%   $34.0316   $34.03   $34.05   $34.00  
  Purchase #6 $183.71   4.346%   $191.694   $191.69   $191.70   $191.70  
  Purchase #7 $21.59   8.846%   $23.4999   $23.50   $23.50   $23.50  
  7 purchase totals = $785.43       $850.7918   $850.79   $850.80   $850.70