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 $112.81   5.764%   $119.3124   $119.31   $119.30   $119.30  
  Purchase #2 $67.87   8.509%   $73.6451   $73.65   $73.65   $73.60  
  Purchase #3 $116.37   11.699%   $129.9841   $129.98   $130.00   $130.00  
  Purchase #4 $187.53   5.451%   $197.7523   $197.75   $197.75   $197.80  
  Purchase #5 $192.84   13.249%   $218.3894   $218.39   $218.40   $218.40  
  Purchase #6 $130.63   3.520%   $135.2282   $135.23   $135.25   $135.20  
  Purchase #7 $71.92   11.561%   $80.2347   $80.23   $80.25   $80.20  
  7 purchase totals = $879.97       $954.5462   $954.54   $954.60   $954.50