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 $134.99   13.309%   $152.9558   $152.96   $152.95   $153.00  
  Purchase #2 $199.85   8.484%   $216.8053   $216.81   $216.80   $216.80  
  Purchase #3 $88.72   10.425%   $97.9691   $97.97   $97.95   $98.00  
  Purchase #4 $93.84   4.712%   $98.2617   $98.26   $98.25   $98.30  
  Purchase #5 $169.90   10.853%   $188.3392   $188.34   $188.35   $188.30  
  Purchase #6 $140.25   13.547%   $159.2497   $159.25   $159.25   $159.20  
  Purchase #7 $232.83   8.417%   $252.4273   $252.43   $252.45   $252.40  
  7 purchase totals = $1,060.38       $1,166.0081   $1,166.02   $1,166.00   $1,166.00