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 $241.44   9.152%   $263.5366   $263.54   $263.55   $263.50  
  Purchase #2 $142.94   11.401%   $159.2366   $159.24   $159.25   $159.20  
  Purchase #3 $18.64   8.349%   $20.1963   $20.20   $20.20   $20.20  
  Purchase #4 $123.96   4.698%   $129.7836   $129.78   $129.80   $129.80  
  Purchase #5 $81.62   10.457%   $90.155   $90.16   $90.15   $90.20  
  Purchase #6 $236.65   9.314%   $258.6916   $258.69   $258.70   $258.70  
  Purchase #7 $117.61   13.160%   $133.0875   $133.09   $133.10   $133.10  
  7 purchase totals = $962.86       $1,054.6872   $1,054.70   $1,054.75   $1,054.70