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 $80.66   13.857%   $91.8371   $91.84   $91.85   $91.80  
  Purchase #2 $194.45   4.726%   $203.6397   $203.64   $203.65   $203.60  
  Purchase #3 $208.59   4.456%   $217.8848   $217.88   $217.90   $217.90  
  Purchase #4 $92.47   3.197%   $95.4263   $95.43   $95.45   $95.40  
  Purchase #5 $208.59   11.848%   $233.3037   $233.30   $233.30   $233.30  
  Purchase #6 $226.92   12.566%   $255.4348   $255.43   $255.45   $255.40  
  Purchase #7 $232.35   3.447%   $240.3591   $240.36   $240.35   $240.40  
  7 purchase totals = $1,244.03       $1,337.8855   $1,337.88   $1,337.95   $1,337.80