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 $173.68   11.301%   $193.3076   $193.31   $193.30   $193.30  
  Purchase #2 $159.95   7.346%   $171.6999   $171.70   $171.70   $171.70  
  Purchase #3 $25.99   13.543%   $29.5098   $29.51   $29.50   $29.50  
  Purchase #4 $92.93   4.721%   $97.3172   $97.32   $97.30   $97.30  
  Purchase #5 $188.35   4.486%   $196.7994   $196.80   $196.80   $196.80  
  Purchase #6 $140.81   6.452%   $149.8951   $149.90   $149.90   $149.90  
  Purchase #7 $191.51   7.766%   $206.3827   $206.38   $206.40   $206.40  
  7 purchase totals = $973.22       $1,044.9117   $1,044.92   $1,044.90   $1,044.90