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 $68.28   7.470%   $73.3805   $73.38   $73.40   $73.40  
  Purchase #2 $45.50   9.621%   $49.8776   $49.88   $49.90   $49.90  
  Purchase #3 $26.99   13.357%   $30.5951   $30.60   $30.60   $30.60  
  Purchase #4 $248.92   11.531%   $277.623   $277.62   $277.60   $277.60  
  Purchase #5 $50.35   11.828%   $56.3054   $56.31   $56.30   $56.30  
  Purchase #6 $204.89   9.161%   $223.66   $223.66   $223.65   $223.70  
  Purchase #7 $224.30   9.534%   $245.6848   $245.68   $245.70   $245.70  
  7 purchase totals = $869.23       $957.1264   $957.13   $957.15   $957.20