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 $86.80   11.421%   $96.7134   $96.71   $96.70   $96.70  
  Purchase #2 $6.30   3.102%   $6.4954   $6.50   $6.50   $6.50  
  Purchase #3 $56.99   5.202%   $59.9546   $59.95   $59.95   $60.00  
  Purchase #4 $248.84   5.807%   $263.2901   $263.29   $263.30   $263.30  
  Purchase #5 $110.77   9.190%   $120.9498   $120.95   $120.95   $120.90  
  Purchase #6 $71.77   11.338%   $79.9073   $79.91   $79.90   $79.90  
  Purchase #7 $105.48   11.372%   $117.4752   $117.48   $117.50   $117.50  
  7 purchase totals = $686.95       $744.7858   $744.79   $744.80   $744.80