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 $58.37   12.209%   $65.4964   $65.50   $65.50   $65.50  
  Purchase #2 $139.67   11.819%   $156.1776   $156.18   $156.20   $156.20  
  Purchase #3 $216.36   3.484%   $223.898   $223.90   $223.90   $223.90  
  Purchase #4 $51.69   8.309%   $55.9849   $55.98   $56.00   $56.00  
  Purchase #5 $102.99   5.133%   $108.2765   $108.28   $108.30   $108.30  
  Purchase #6 $27.86   11.102%   $30.953   $30.95   $30.95   $31.00  
  Purchase #7 $80.61   13.216%   $91.2634   $91.26   $91.25   $91.30  
  7 purchase totals = $677.55       $732.0498   $732.05   $732.10   $732.20