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 $8.57   4.549%   $8.9598   $8.96   $8.95   $9.00  
  Purchase #2 $40.77   5.411%   $42.9761   $42.98   $43.00   $43.00  
  Purchase #3 $120.95   13.658%   $137.4694   $137.47   $137.45   $137.50  
  Purchase #4 $27.55   12.687%   $31.0453   $31.05   $31.05   $31.00  
  Purchase #5 $206.81   10.675%   $228.887   $228.89   $228.90   $228.90  
  Purchase #6 $22.26   4.864%   $23.3427   $23.34   $23.35   $23.30  
  Purchase #7 $151.63   4.103%   $157.8514   $157.85   $157.85   $157.90  
  7 purchase totals = $578.54       $630.5317   $630.54   $630.55   $630.60