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 $242.35   9.858%   $266.2409   $266.24   $266.25   $266.20  
  Purchase #2 $112.56   3.236%   $116.2024   $116.20   $116.20   $116.20  
  Purchase #3 $112.43   5.835%   $118.9903   $118.99   $119.00   $119.00  
  Purchase #4 $143.38   13.233%   $162.3535   $162.35   $162.35   $162.40  
  Purchase #5 $237.95   8.435%   $258.0211   $258.02   $258.00   $258.00  
  Purchase #6 $185.49   10.295%   $204.5862   $204.59   $204.60   $204.60  
  Purchase #7 $116.53   6.640%   $124.2676   $124.27   $124.25   $124.30  
  7 purchase totals = $1,150.69       $1,250.6620   $1,250.66   $1,250.65   $1,250.70