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 $214.47   9.201%   $234.2034   $234.20   $234.20   $234.20  
  Purchase #2 $76.53   11.257%   $85.145   $85.15   $85.15   $85.10  
  Purchase #3 $157.89   6.381%   $167.965   $167.97   $167.95   $168.00  
  Purchase #4 $14.50   5.697%   $15.3261   $15.33   $15.35   $15.30  
  Purchase #5 $230.95   10.163%   $254.4214   $254.42   $254.40   $254.40  
  Purchase #6 $78.27   12.872%   $88.3449   $88.34   $88.35   $88.30  
  Purchase #7 $13.99   7.377%   $15.022   $15.02   $15.00   $15.00  
  7 purchase totals = $786.60       $860.4278   $860.43   $860.40   $860.30