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 $54.71   4.873%   $57.376   $57.38   $57.40   $57.40  
  Purchase #2 $156.45   12.870%   $176.5851   $176.59   $176.60   $176.60  
  Purchase #3 $151.98   3.596%   $157.4452   $157.45   $157.45   $157.40  
  Purchase #4 $26.49   5.381%   $27.9154   $27.92   $27.90   $27.90  
  Purchase #5 $64.39   6.206%   $68.386   $68.39   $68.40   $68.40  
  Purchase #6 $107.98   5.582%   $114.0074   $114.01   $114.00   $114.00  
  Purchase #7 $48.31   5.409%   $50.9231   $50.92   $50.90   $50.90  
  7 purchase totals = $610.31       $652.6382   $652.66   $652.65   $652.60