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 $14.41   5.761%   $15.2402   $15.24   $15.25   $15.20  
  Purchase #2 $26.82   5.646%   $28.3343   $28.33   $28.35   $28.30  
  Purchase #3 $234.26   4.283%   $244.2934   $244.29   $244.30   $244.30  
  Purchase #4 $166.45   12.351%   $187.0082   $187.01   $187.00   $187.00  
  Purchase #5 $194.41   12.292%   $218.3069   $218.31   $218.30   $218.30  
  Purchase #6 $34.90   5.308%   $36.7525   $36.75   $36.75   $36.80  
  Purchase #7 $29.91   3.470%   $30.9479   $30.95   $30.95   $30.90  
  7 purchase totals = $701.16       $760.8834   $760.88   $760.90   $760.80