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 $141.61   6.424%   $150.707   $150.71   $150.70   $150.70  
  Purchase #2 $247.60   4.585%   $258.9525   $258.95   $258.95   $259.00  
  Purchase #3 $22.32   6.828%   $23.844   $23.84   $23.85   $23.80  
  Purchase #4 $211.90   10.262%   $233.6452   $233.65   $233.65   $233.60  
  Purchase #5 $30.39   12.292%   $34.1255   $34.13   $34.15   $34.10  
  Purchase #6 $85.74   8.357%   $92.9053   $92.91   $92.90   $92.90  
  Purchase #7 $140.75   13.741%   $160.0905   $160.09   $160.10   $160.10  
  7 purchase totals = $880.31       $954.2700   $954.28   $954.30   $954.20