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 $62.47   6.672%   $66.638   $66.64   $66.65   $66.60  
  Purchase #2 $84.80   8.670%   $92.1522   $92.15   $92.15   $92.20  
  Purchase #3 $244.49   3.702%   $253.541   $253.54   $253.55   $253.50  
  Purchase #4 $191.84   7.750%   $206.7076   $206.71   $206.70   $206.70  
  Purchase #5 $47.33   8.418%   $51.3142   $51.31   $51.30   $51.30  
  Purchase #6 $7.74   13.126%   $8.756   $8.76   $8.75   $8.80  
  Purchase #7 $70.28   8.791%   $76.4583   $76.46   $76.45   $76.50  
  7 purchase totals = $708.95       $755.5673   $755.57   $755.55   $755.60