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 $239.33   11.671%   $267.2622   $267.26   $267.25   $267.30  
  Purchase #2 $17.82   9.317%   $19.4803   $19.48   $19.50   $19.50  
  Purchase #3 $162.70   9.529%   $178.2037   $178.20   $178.20   $178.20  
  Purchase #4 $125.90   12.741%   $141.9409   $141.94   $141.95   $141.90  
  Purchase #5 $171.36   3.188%   $176.823   $176.82   $176.80   $176.80  
  Purchase #6 $165.96   7.574%   $178.5298   $178.53   $178.55   $178.50  
  Purchase #7 $123.60   10.672%   $136.7906   $136.79   $136.80   $136.80  
  7 purchase totals = $1,006.67       $1,099.0305   $1,099.02   $1,099.05   $1,099.00