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 $29.41   9.500%   $32.204   $32.20   $32.20   $32.20  
  Purchase #2 $116.61   8.349%   $126.3458   $126.35   $126.35   $126.30  
  Purchase #3 $247.75   9.551%   $271.4126   $271.41   $271.40   $271.40  
  Purchase #4 $174.45   7.370%   $187.307   $187.31   $187.30   $187.30  
  Purchase #5 $186.48   3.747%   $193.4674   $193.47   $193.45   $193.50  
  Purchase #6 $20.31   11.154%   $22.5754   $22.58   $22.60   $22.60  
  Purchase #7 $64.73   13.368%   $73.3831   $73.38   $73.40   $73.40  
  7 purchase totals = $839.74       $906.6953   $906.70   $906.70   $906.70