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 $59.25   12.229%   $66.4957   $66.50   $66.50   $66.50  
  Purchase #2 $195.77   9.572%   $214.5091   $214.51   $214.50   $214.50  
  Purchase #3 $152.34   9.729%   $167.1612   $167.16   $167.15   $167.20  
  Purchase #4 $24.89   7.413%   $26.7351   $26.74   $26.75   $26.70  
  Purchase #5 $220.93   10.715%   $244.6026   $244.60   $244.60   $244.60  
  Purchase #6 $170.67   12.859%   $192.6165   $192.62   $192.60   $192.60  
  Purchase #7 $197.57   9.247%   $215.8393   $215.84   $215.85   $215.80  
  7 purchase totals = $1,021.42       $1,127.9595   $1,127.97   $1,127.95   $1,127.90