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 $248.46   7.467%   $267.0125   $267.01   $267.00   $267.00  
  Purchase #2 $71.29   5.263%   $75.042   $75.04   $75.05   $75.00  
  Purchase #3 $166.79   4.335%   $174.0203   $174.02   $174.00   $174.00  
  Purchase #4 $13.38   11.857%   $14.9665   $14.97   $14.95   $15.00  
  Purchase #5 $58.44   3.382%   $60.4164   $60.42   $60.40   $60.40  
  Purchase #6 $116.81   12.719%   $131.6671   $131.67   $131.65   $131.70  
  Purchase #7 $123.76   5.184%   $130.1757   $130.18   $130.20   $130.20  
  7 purchase totals = $798.93       $853.3005   $853.31   $853.25   $853.30