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 $87.57   9.516%   $95.9032   $95.90   $95.90   $95.90  
  Purchase #2 $48.48   3.624%   $50.2369   $50.24   $50.25   $50.20  
  Purchase #3 $5.91   12.193%   $6.6306   $6.63   $6.65   $6.60  
  Purchase #4 $86.61   9.288%   $94.6543   $94.65   $94.65   $94.70  
  Purchase #5 $247.62   5.254%   $260.63   $260.63   $260.65   $260.60  
  Purchase #6 $179.96   7.522%   $193.4966   $193.50   $193.50   $193.50  
  Purchase #7 $37.49   10.641%   $41.4793   $41.48   $41.50   $41.50  
  7 purchase totals = $693.64       $743.0309   $743.03   $743.10   $743.00