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 $67.99   8.230%   $73.5856   $73.59   $73.60   $73.60  
  Purchase #2 $209.83   6.512%   $223.4941   $223.49   $223.50   $223.50  
  Purchase #3 $51.87   5.573%   $54.7607   $54.76   $54.75   $54.80  
  Purchase #4 $20.98   9.515%   $22.9762   $22.98   $23.00   $23.00  
  Purchase #5 $151.78   3.407%   $156.9511   $156.95   $156.95   $157.00  
  Purchase #6 $54.66   5.596%   $57.7188   $57.72   $57.70   $57.70  
  Purchase #7 $163.93   3.191%   $169.161   $169.16   $169.15   $169.20  
  7 purchase totals = $721.04       $758.6475   $758.65   $758.65   $758.80