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 $248.43   5.598%   $262.3371   $262.34   $262.35   $262.30  
  Purchase #2 $164.84   13.201%   $186.6005   $186.60   $186.60   $186.60  
  Purchase #3 $186.70   9.751%   $204.9051   $204.91   $204.90   $204.90  
  Purchase #4 $220.99   9.842%   $242.7398   $242.74   $242.75   $242.70  
  Purchase #5 $126.67   8.801%   $137.8182   $137.82   $137.80   $137.80  
  Purchase #6 $198.61   9.323%   $217.1264   $217.13   $217.15   $217.10  
  Purchase #7 $24.93   13.281%   $28.241   $28.24   $28.25   $28.20  
  7 purchase totals = $1,171.17       $1,279.7681   $1,279.78   $1,279.80   $1,279.60