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 $108.37   5.437%   $114.2621   $114.26   $114.25   $114.30  
  Purchase #2 $136.42   12.208%   $153.0742   $153.07   $153.05   $153.10  
  Purchase #3 $195.76   5.682%   $206.8831   $206.88   $206.90   $206.90  
  Purchase #4 $115.95   5.474%   $122.2971   $122.30   $122.30   $122.30  
  Purchase #5 $14.54   11.463%   $16.2067   $16.21   $16.20   $16.20  
  Purchase #6 $72.97   3.107%   $75.2372   $75.24   $75.25   $75.20  
  Purchase #7 $56.35   11.871%   $63.0393   $63.04   $63.05   $63.00  
  7 purchase totals = $700.36       $750.9997   $751.00   $751.00   $751.00