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 $69.33   5.297%   $73.0024   $73.00   $73.00   $73.00  
  Purchase #2 $233.82   6.461%   $248.9271   $248.93   $248.95   $248.90  
  Purchase #3 $151.28   12.219%   $169.7649   $169.76   $169.75   $169.80  
  Purchase #4 $160.43   10.594%   $177.426   $177.43   $177.45   $177.40  
  Purchase #5 $57.37   13.734%   $65.2492   $65.25   $65.25   $65.20  
  Purchase #6 $39.54   9.432%   $43.2694   $43.27   $43.25   $43.30  
  Purchase #7 $177.62   3.796%   $184.3625   $184.36   $184.35   $184.40  
  7 purchase totals = $889.39       $962.0015   $962.00   $962.00   $962.00