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 $112.40   12.147%   $126.0532   $126.05   $126.05   $126.10  
  Purchase #2 $217.93   7.151%   $233.5142   $233.51   $233.50   $233.50  
  Purchase #3 $132.71   4.252%   $138.3528   $138.35   $138.35   $138.40  
  Purchase #4 $56.34   8.266%   $60.9971   $61.00   $61.00   $61.00  
  Purchase #5 $21.53   13.510%   $24.4387   $24.44   $24.45   $24.40  
  Purchase #6 $133.39   5.797%   $141.1226   $141.12   $141.10   $141.10  
  Purchase #7 $147.61   11.174%   $164.1039   $164.10   $164.10   $164.10  
  7 purchase totals = $821.91       $888.5825   $888.57   $888.55   $888.60