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 $111.30   13.750%   $126.6038   $126.60   $126.60   $126.60  
  Purchase #2 $71.99   8.415%   $78.048   $78.05   $78.05   $78.00  
  Purchase #3 $81.76   5.157%   $85.9764   $85.98   $86.00   $86.00  
  Purchase #4 $140.55   13.315%   $159.2642   $159.26   $159.25   $159.30  
  Purchase #5 $51.64   4.384%   $53.9039   $53.90   $53.90   $53.90  
  Purchase #6 $64.41   3.372%   $66.5819   $66.58   $66.60   $66.60  
  Purchase #7 $232.90   11.556%   $259.8139   $259.81   $259.80   $259.80  
  7 purchase totals = $754.55       $830.1921   $830.18   $830.20   $830.20