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 $131.52   13.141%   $148.803   $148.80   $148.80   $148.80  
  Purchase #2 $80.48   5.597%   $84.9845   $84.98   $85.00   $85.00  
  Purchase #3 $151.58   10.190%   $167.026   $167.03   $167.05   $167.00  
  Purchase #4 $205.73   4.299%   $214.5743   $214.57   $214.55   $214.60  
  Purchase #5 $54.25   4.808%   $56.8583   $56.86   $56.85   $56.90  
  Purchase #6 $119.36   13.575%   $135.5631   $135.56   $135.55   $135.60  
  Purchase #7 $95.59   3.139%   $98.5906   $98.59   $98.60   $98.60  
  7 purchase totals = $838.51       $906.3998   $906.39   $906.40   $906.50