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 $26.65   11.218%   $29.6396   $29.64   $29.65   $29.60  
  Purchase #2 $83.69   13.780%   $95.2225   $95.22   $95.20   $95.20  
  Purchase #3 $67.57   13.577%   $76.744   $76.74   $76.75   $76.70  
  Purchase #4 $75.34   10.507%   $83.256   $83.26   $83.25   $83.30  
  Purchase #5 $225.49   7.148%   $241.608   $241.61   $241.60   $241.60  
  Purchase #6 $156.26   7.279%   $167.6342   $167.63   $167.65   $167.60  
  Purchase #7 $43.59   9.264%   $47.6282   $47.63   $47.65   $47.60  
  7 purchase totals = $678.59       $741.7325   $741.73   $741.75   $741.60