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 $87.63   8.719%   $95.2705   $95.27   $95.25   $95.30  
  Purchase #2 $14.95   10.111%   $16.4616   $16.46   $16.45   $16.50  
  Purchase #3 $156.56   9.411%   $171.2939   $171.29   $171.30   $171.30  
  Purchase #4 $159.82   4.357%   $166.7834   $166.78   $166.80   $166.80  
  Purchase #5 $94.38   11.115%   $104.8703   $104.87   $104.85   $104.90  
  Purchase #6 $31.84   9.348%   $34.8164   $34.82   $34.80   $34.80  
  Purchase #7 $177.93   9.858%   $195.4703   $195.47   $195.45   $195.50  
  7 purchase totals = $723.11       $784.9664   $784.96   $784.90   $785.10