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 $61.74   11.113%   $68.6012   $68.60   $68.60   $68.60  
  Purchase #2 $167.93   13.859%   $191.2034   $191.20   $191.20   $191.20  
  Purchase #3 $148.59   6.551%   $158.3241   $158.32   $158.30   $158.30  
  Purchase #4 $147.46   5.858%   $156.0982   $156.10   $156.10   $156.10  
  Purchase #5 $81.66   3.432%   $84.4626   $84.46   $84.45   $84.50  
  Purchase #6 $84.76   13.145%   $95.9017   $95.90   $95.90   $95.90  
  Purchase #7 $25.42   3.490%   $26.3072   $26.31   $26.30   $26.30  
  7 purchase totals = $717.56       $780.8984   $780.89   $780.85   $780.90