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 $244.83   11.481%   $272.9389   $272.94   $272.95   $272.90  
  Purchase #2 $194.26   13.145%   $219.7955   $219.80   $219.80   $219.80  
  Purchase #3 $101.66   12.694%   $114.5647   $114.56   $114.55   $114.60  
  Purchase #4 $117.93   12.717%   $132.9272   $132.93   $132.95   $132.90  
  Purchase #5 $157.86   11.651%   $176.2523   $176.25   $176.25   $176.30  
  Purchase #6 $183.96   5.371%   $193.8405   $193.84   $193.85   $193.80  
  Purchase #7 $138.70   8.838%   $150.9583   $150.96   $150.95   $151.00  
  7 purchase totals = $1,139.20       $1,261.2774   $1,261.28   $1,261.30   $1,261.30