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 $207.53   12.861%   $234.2204   $234.22   $234.20   $234.20  
  Purchase #2 $118.98   4.675%   $124.5423   $124.54   $124.55   $124.50  
  Purchase #3 $13.45   3.863%   $13.9696   $13.97   $13.95   $14.00  
  Purchase #4 $177.43   9.248%   $193.8387   $193.84   $193.85   $193.80  
  Purchase #5 $199.41   11.816%   $222.9723   $222.97   $222.95   $223.00  
  Purchase #6 $54.47   6.534%   $58.0291   $58.03   $58.05   $58.00  
  Purchase #7 $60.96   5.720%   $64.4469   $64.45   $64.45   $64.40  
  7 purchase totals = $832.23       $912.0193   $912.02   $912.00   $911.90