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 $35.45   6.343%   $37.6986   $37.70   $37.70   $37.70  
  Purchase #2 $119.38   4.539%   $124.7987   $124.80   $124.80   $124.80  
  Purchase #3 $220.55   7.623%   $237.3625   $237.36   $237.35   $237.40  
  Purchase #4 $86.73   8.352%   $93.9737   $93.97   $93.95   $94.00  
  Purchase #5 $217.43   12.792%   $245.2436   $245.24   $245.25   $245.20  
  Purchase #6 $208.40   3.125%   $214.9125   $214.91   $214.90   $214.90  
  Purchase #7 $65.60   10.494%   $72.4841   $72.48   $72.50   $72.50  
  7 purchase totals = $953.54       $1,026.4737   $1,026.46   $1,026.45   $1,026.50