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 $160.60   9.417%   $175.7237   $175.72   $175.70   $175.70  
  Purchase #2 $224.46   7.356%   $240.9713   $240.97   $240.95   $241.00  
  Purchase #3 $54.75   5.731%   $57.8877   $57.89   $57.90   $57.90  
  Purchase #4 $141.90   13.701%   $161.3417   $161.34   $161.35   $161.30  
  Purchase #5 $115.58   8.396%   $125.2841   $125.28   $125.30   $125.30  
  Purchase #6 $58.63   10.110%   $64.5575   $64.56   $64.55   $64.60  
  Purchase #7 $237.84   10.255%   $262.2305   $262.23   $262.25   $262.20  
  7 purchase totals = $993.76       $1,087.9965   $1,087.99   $1,088.00   $1,088.00