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 $245.65   12.601%   $276.6044   $276.60   $276.60   $276.60  
  Purchase #2 $67.83   4.556%   $70.9203   $70.92   $70.90   $70.90  
  Purchase #3 $215.96   5.515%   $227.8702   $227.87   $227.85   $227.90  
  Purchase #4 $141.56   7.549%   $152.2464   $152.25   $152.25   $152.20  
  Purchase #5 $96.78   3.281%   $99.9554   $99.96   $99.95   $100.00  
  Purchase #6 $172.66   12.301%   $193.8989   $193.90   $193.90   $193.90  
  Purchase #7 $216.37   12.854%   $244.1822   $244.18   $244.20   $244.20  
  7 purchase totals = $1,156.81       $1,265.6778   $1,265.68   $1,265.65   $1,265.70