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 $88.25   11.649%   $98.5302   $98.53   $98.55   $98.50  
  Purchase #2 $79.61   3.353%   $82.2793   $82.28   $82.30   $82.30  
  Purchase #3 $108.30   8.416%   $117.4145   $117.41   $117.40   $117.40  
  Purchase #4 $116.55   8.873%   $126.8915   $126.89   $126.90   $126.90  
  Purchase #5 $33.39   5.401%   $35.1934   $35.19   $35.20   $35.20  
  Purchase #6 $212.30   6.126%   $225.3055   $225.31   $225.30   $225.30  
  Purchase #7 $80.49   5.182%   $84.661   $84.66   $84.65   $84.70  
  7 purchase totals = $718.89       $770.2754   $770.27   $770.30   $770.30