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 $155.39   7.223%   $166.6138   $166.61   $166.60   $166.60  
  Purchase #2 $202.62   6.293%   $215.3709   $215.37   $215.35   $215.40  
  Purchase #3 $95.63   3.502%   $98.979   $98.98   $99.00   $99.00  
  Purchase #4 $56.48   12.528%   $63.5558   $63.56   $63.55   $63.60  
  Purchase #5 $122.90   8.358%   $133.172   $133.17   $133.15   $133.20  
  Purchase #6 $217.67   3.152%   $224.531   $224.53   $224.55   $224.50  
  Purchase #7 $130.34   9.122%   $142.2296   $142.23   $142.25   $142.20  
  7 purchase totals = $981.03       $1,044.4521   $1,044.45   $1,044.45   $1,044.50