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 $76.40   11.293%   $85.0279   $85.03   $85.05   $85.00  
  Purchase #2 $101.94   13.192%   $115.3879   $115.39   $115.40   $115.40  
  Purchase #3 $56.93   3.283%   $58.799   $58.80   $58.80   $58.80  
  Purchase #4 $160.97   6.420%   $171.3043   $171.30   $171.30   $171.30  
  Purchase #5 $166.57   5.866%   $176.341   $176.34   $176.35   $176.30  
  Purchase #6 $6.88   4.710%   $7.204   $7.20   $7.20   $7.20  
  Purchase #7 $141.28   6.293%   $150.1708   $150.17   $150.15   $150.20  
  7 purchase totals = $710.97       $764.2349   $764.23   $764.25   $764.20