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 $30.62   5.835%   $32.4067   $32.41   $32.40   $32.40  
  Purchase #2 $91.83   3.860%   $95.3746   $95.37   $95.35   $95.40  
  Purchase #3 $25.28   5.414%   $26.6487   $26.65   $26.65   $26.60  
  Purchase #4 $96.49   3.372%   $99.7436   $99.74   $99.75   $99.70  
  Purchase #5 $72.33   5.606%   $76.3848   $76.38   $76.40   $76.40  
  Purchase #6 $43.85   8.317%   $47.497   $47.50   $47.50   $47.50  
  Purchase #7 $207.90   4.863%   $218.0102   $218.01   $218.00   $218.00  
  7 purchase totals = $568.30       $596.0656   $596.06   $596.05   $596.00