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 $119.76   3.514%   $123.9684   $123.97   $123.95   $124.00  
  Purchase #2 $175.77   4.684%   $184.0031   $184.00   $184.00   $184.00  
  Purchase #3 $133.96   7.450%   $143.94   $143.94   $143.95   $143.90  
  Purchase #4 $249.34   10.535%   $275.608   $275.61   $275.60   $275.60  
  Purchase #5 $17.51   7.649%   $18.8493   $18.85   $18.85   $18.80  
  Purchase #6 $119.38   11.713%   $133.363   $133.36   $133.35   $133.40  
  Purchase #7 $199.74   11.679%   $223.0676   $223.07   $223.05   $223.10  
  7 purchase totals = $1,015.46       $1,102.7994   $1,102.80   $1,102.75   $1,102.80