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 $249.29   6.783%   $266.1993   $266.20   $266.20   $266.20  
  Purchase #2 $122.44   3.668%   $126.9311   $126.93   $126.95   $126.90  
  Purchase #3 $5.96   3.556%   $6.1719   $6.17   $6.15   $6.20  
  Purchase #4 $127.44   6.535%   $135.7682   $135.77   $135.75   $135.80  
  Purchase #5 $204.49   8.388%   $221.6426   $221.64   $221.65   $221.60  
  Purchase #6 $78.70   4.199%   $82.0046   $82.00   $82.00   $82.00  
  Purchase #7 $33.80   5.357%   $35.6107   $35.61   $35.60   $35.60  
  7 purchase totals = $822.12       $874.3284   $874.32   $874.30   $874.30