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 $5.47   9.553%   $5.9925   $5.99   $6.00   $6.00  
  Purchase #2 $50.92   11.151%   $56.5981   $56.60   $56.60   $56.60  
  Purchase #3 $176.62   5.258%   $185.9067   $185.91   $185.90   $185.90  
  Purchase #4 $86.92   5.153%   $91.399   $91.40   $91.40   $91.40  
  Purchase #5 $225.57   3.321%   $233.0612   $233.06   $233.05   $233.10  
  Purchase #6 $159.76   7.533%   $171.7947   $171.79   $171.80   $171.80  
  Purchase #7 $247.29   7.693%   $266.314   $266.31   $266.30   $266.30  
  7 purchase totals = $952.55       $1,011.0662   $1,011.06   $1,011.05   $1,011.10