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 $98.66   6.120%   $104.698   $104.70   $104.70   $104.70  
  Purchase #2 $196.95   3.312%   $203.473   $203.47   $203.45   $203.50  
  Purchase #3 $194.26   6.234%   $206.3702   $206.37   $206.35   $206.40  
  Purchase #4 $21.81   12.840%   $24.6104   $24.61   $24.60   $24.60  
  Purchase #5 $51.64   13.807%   $58.7699   $58.77   $58.75   $58.80  
  Purchase #6 $106.59   4.718%   $111.6189   $111.62   $111.60   $111.60  
  Purchase #7 $109.76   12.240%   $123.1946   $123.19   $123.20   $123.20  
  7 purchase totals = $779.67       $832.7350   $832.73   $832.65   $832.80