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 $230.99   10.266%   $254.7034   $254.70   $254.70   $254.70  
  Purchase #2 $197.86   9.398%   $216.4549   $216.45   $216.45   $216.50  
  Purchase #3 $171.95   12.329%   $193.1497   $193.15   $193.15   $193.10  
  Purchase #4 $25.56   4.613%   $26.7391   $26.74   $26.75   $26.70  
  Purchase #5 $154.26   8.532%   $167.4215   $167.42   $167.40   $167.40  
  Purchase #6 $175.74   10.344%   $193.9185   $193.92   $193.90   $193.90  
  Purchase #7 $187.71   10.224%   $206.9015   $206.90   $206.90   $206.90  
  7 purchase totals = $1,144.07       $1,259.2886   $1,259.28   $1,259.25   $1,259.20