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 $247.36   11.160%   $274.9654   $274.97   $274.95   $275.00  
  Purchase #2 $116.61   5.730%   $123.2918   $123.29   $123.30   $123.30  
  Purchase #3 $64.61   4.834%   $67.7332   $67.73   $67.75   $67.70  
  Purchase #4 $89.76   9.172%   $97.9928   $97.99   $98.00   $98.00  
  Purchase #5 $36.61   13.614%   $41.5941   $41.59   $41.60   $41.60  
  Purchase #6 $196.38   11.727%   $219.4095   $219.41   $219.40   $219.40  
  Purchase #7 $195.94   4.604%   $204.9611   $204.96   $204.95   $205.00  
  7 purchase totals = $947.27       $1,029.9479   $1,029.94   $1,029.95   $1,030.00