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 $60.74   11.323%   $67.6176   $67.62   $67.60   $67.60  
  Purchase #2 $20.85   9.609%   $22.8535   $22.85   $22.85   $22.90  
  Purchase #3 $64.93   6.670%   $69.2608   $69.26   $69.25   $69.30  
  Purchase #4 $227.41   7.870%   $245.3072   $245.31   $245.30   $245.30  
  Purchase #5 $79.25   6.866%   $84.6913   $84.69   $84.70   $84.70  
  Purchase #6 $152.60   8.711%   $165.893   $165.89   $165.90   $165.90  
  Purchase #7 $15.70   3.619%   $16.2682   $16.27   $16.25   $16.30  
  7 purchase totals = $621.48       $671.8916   $671.89   $671.85   $672.00