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 $176.67   10.755%   $195.6709   $195.67   $195.65   $195.70  
  Purchase #2 $76.86   11.378%   $85.6051   $85.61   $85.60   $85.60  
  Purchase #3 $97.60   3.856%   $101.3635   $101.36   $101.35   $101.40  
  Purchase #4 $214.56   7.311%   $230.2465   $230.25   $230.25   $230.20  
  Purchase #5 $101.49   4.218%   $105.7708   $105.77   $105.75   $105.80  
  Purchase #6 $92.95   7.335%   $99.7679   $99.77   $99.75   $99.80  
  Purchase #7 $145.88   7.360%   $156.6168   $156.62   $156.60   $156.60  
  7 purchase totals = $906.01       $975.0415   $975.05   $974.95   $975.10