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 $81.58   13.820%   $92.8544   $92.85   $92.85   $92.90  
  Purchase #2 $235.47   11.454%   $262.4407   $262.44   $262.45   $262.40  
  Purchase #3 $194.37   10.842%   $215.4436   $215.44   $215.45   $215.40  
  Purchase #4 $73.87   3.511%   $76.4636   $76.46   $76.45   $76.50  
  Purchase #5 $178.35   8.548%   $193.5954   $193.60   $193.60   $193.60  
  Purchase #6 $134.96   11.632%   $150.6585   $150.66   $150.65   $150.70  
  Purchase #7 $249.43   12.680%   $281.0577   $281.06   $281.05   $281.10  
  7 purchase totals = $1,148.03       $1,272.5139   $1,272.51   $1,272.50   $1,272.60