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 $203.61   7.373%   $218.6222   $218.62   $218.60   $218.60  
  Purchase #2 $60.69   9.119%   $66.2243   $66.22   $66.20   $66.20  
  Purchase #3 $246.83   10.759%   $273.3864   $273.39   $273.40   $273.40  
  Purchase #4 $229.85   7.561%   $247.229   $247.23   $247.25   $247.20  
  Purchase #5 $152.71   3.504%   $158.061   $158.06   $158.05   $158.10  
  Purchase #6 $75.83   13.177%   $85.8221   $85.82   $85.80   $85.80  
  Purchase #7 $131.26   3.238%   $135.5102   $135.51   $135.50   $135.50  
  7 purchase totals = $1,100.78       $1,184.8552   $1,184.85   $1,184.80   $1,184.80