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 $66.39   13.470%   $75.3327   $75.33   $75.35   $75.30  
  Purchase #2 $69.38   6.484%   $73.8786   $73.88   $73.90   $73.90  
  Purchase #3 $135.71   4.660%   $142.0341   $142.03   $142.05   $142.00  
  Purchase #4 $169.76   3.755%   $176.1345   $176.13   $176.15   $176.10  
  Purchase #5 $245.98   9.714%   $269.8745   $269.87   $269.85   $269.90  
  Purchase #6 $96.31   7.302%   $103.3426   $103.34   $103.35   $103.30  
  Purchase #7 $205.29   9.372%   $224.5298   $224.53   $224.55   $224.50  
  7 purchase totals = $988.82       $1,065.1268   $1,065.11   $1,065.20   $1,065.00