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 $65.53   10.610%   $72.4827   $72.48   $72.50   $72.50  
  Purchase #2 $213.59   13.148%   $241.6728   $241.67   $241.65   $241.70  
  Purchase #3 $249.90   8.815%   $271.9287   $271.93   $271.95   $271.90  
  Purchase #4 $53.62   8.774%   $58.3246   $58.32   $58.30   $58.30  
  Purchase #5 $24.50   10.602%   $27.0975   $27.10   $27.10   $27.10  
  Purchase #6 $50.84   10.252%   $56.0521   $56.05   $56.05   $56.10  
  Purchase #7 $55.82   4.352%   $58.2493   $58.25   $58.25   $58.20  
  7 purchase totals = $713.80       $785.8077   $785.80   $785.80   $785.80