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 $208.35   7.316%   $223.5929   $223.59   $223.60   $223.60  
  Purchase #2 $53.46   9.594%   $58.589   $58.59   $58.60   $58.60  
  Purchase #3 $65.55   5.444%   $69.1185   $69.12   $69.10   $69.10  
  Purchase #4 $168.33   5.683%   $177.8962   $177.90   $177.90   $177.90  
  Purchase #5 $98.38   7.366%   $105.6267   $105.63   $105.65   $105.60  
  Purchase #6 $225.33   7.792%   $242.8877   $242.89   $242.90   $242.90  
  Purchase #7 $14.27   13.531%   $16.2009   $16.20   $16.20   $16.20  
  7 purchase totals = $833.67       $893.9119   $893.92   $893.95   $893.90