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 $246.78   10.679%   $273.1336   $273.13   $273.15   $273.10  
  Purchase #2 $186.73   4.595%   $195.3102   $195.31   $195.30   $195.30  
  Purchase #3 $70.35   4.730%   $73.6776   $73.68   $73.70   $73.70  
  Purchase #4 $161.27   3.824%   $167.437   $167.44   $167.45   $167.40  
  Purchase #5 $197.99   4.865%   $207.6222   $207.62   $207.60   $207.60  
  Purchase #6 $146.33   3.312%   $151.1764   $151.18   $151.20   $151.20  
  Purchase #7 $62.30   13.730%   $70.8538   $70.85   $70.85   $70.90  
  7 purchase totals = $1,071.75       $1,139.2108   $1,139.21   $1,139.25   $1,139.20