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 $68.34   4.172%   $71.1911   $71.19   $71.20   $71.20  
  Purchase #2 $176.78   5.392%   $186.312   $186.31   $186.30   $186.30  
  Purchase #3 $14.78   9.812%   $16.2302   $16.23   $16.25   $16.20  
  Purchase #4 $75.48   6.398%   $80.3092   $80.31   $80.30   $80.30  
  Purchase #5 $197.84   3.867%   $205.4905   $205.49   $205.50   $205.50  
  Purchase #6 $249.85   4.781%   $261.7953   $261.80   $261.80   $261.80  
  Purchase #7 $94.53   4.128%   $98.4322   $98.43   $98.45   $98.40  
  7 purchase totals = $877.60       $919.7605   $919.76   $919.80   $919.70