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 $57.59   13.269%   $65.2316   $65.23   $65.25   $65.20  
  Purchase #2 $123.87   7.693%   $133.3993   $133.40   $133.40   $133.40  
  Purchase #3 $91.27   6.274%   $96.9963   $97.00   $97.00   $97.00  
  Purchase #4 $159.31   5.295%   $167.7455   $167.75   $167.75   $167.70  
  Purchase #5 $126.84   10.821%   $140.5654   $140.57   $140.55   $140.60  
  Purchase #6 $244.31   8.396%   $264.8223   $264.82   $264.80   $264.80  
  Purchase #7 $80.94   6.752%   $86.4051   $86.41   $86.40   $86.40  
  7 purchase totals = $884.13       $955.1655   $955.18   $955.15   $955.10