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 $84.99   13.476%   $96.4433   $96.44   $96.45   $96.40  
  Purchase #2 $200.50   3.172%   $206.8599   $206.86   $206.85   $206.90  
  Purchase #3 $35.80   10.348%   $39.5046   $39.50   $39.50   $39.50  
  Purchase #4 $92.46   7.668%   $99.5498   $99.55   $99.55   $99.50  
  Purchase #5 $211.26   9.451%   $231.2262   $231.23   $231.25   $231.20  
  Purchase #6 $24.42   3.507%   $25.2764   $25.28   $25.30   $25.30  
  Purchase #7 $61.97   12.836%   $69.9245   $69.92   $69.90   $69.90  
  7 purchase totals = $711.40       $768.7847   $768.78   $768.80   $768.70