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 $215.58   12.188%   $241.8549   $241.85   $241.85   $241.90  
  Purchase #2 $219.67   13.669%   $249.6967   $249.70   $249.70   $249.70  
  Purchase #3 $200.58   6.215%   $213.046   $213.05   $213.05   $213.00  
  Purchase #4 $29.69   4.595%   $31.0543   $31.05   $31.05   $31.10  
  Purchase #5 $49.35   12.720%   $55.6273   $55.63   $55.65   $55.60  
  Purchase #6 $7.25   11.281%   $8.0679   $8.07   $8.05   $8.10  
  Purchase #7 $103.25   12.713%   $116.3762   $116.38   $116.40   $116.40  
  7 purchase totals = $825.37       $915.7233   $915.73   $915.75   $915.80