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 $63.62   7.741%   $68.5448   $68.54   $68.55   $68.50  
  Purchase #2 $183.48   12.267%   $205.9875   $205.99   $206.00   $206.00  
  Purchase #3 $44.40   7.129%   $47.5653   $47.57   $47.55   $47.60  
  Purchase #4 $239.38   12.336%   $268.9099   $268.91   $268.90   $268.90  
  Purchase #5 $9.75   9.808%   $10.7063   $10.71   $10.70   $10.70  
  Purchase #6 $65.51   5.532%   $69.134   $69.13   $69.15   $69.10  
  Purchase #7 $147.46   3.864%   $153.1579   $153.16   $153.15   $153.20  
  7 purchase totals = $753.60       $824.0057   $824.01   $824.00   $824.00