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 $12.59   3.455%   $13.025   $13.03   $13.05   $13.00  
  Purchase #2 $90.45   7.597%   $97.3215   $97.32   $97.30   $97.30  
  Purchase #3 $147.62   6.551%   $157.2906   $157.29   $157.30   $157.30  
  Purchase #4 $20.37   3.158%   $21.0133   $21.01   $21.00   $21.00  
  Purchase #5 $188.70   10.277%   $208.0927   $208.09   $208.10   $208.10  
  Purchase #6 $18.80   12.118%   $21.0782   $21.08   $21.10   $21.10  
  Purchase #7 $198.74   7.723%   $214.0887   $214.09   $214.10   $214.10  
  7 purchase totals = $677.27       $731.9100   $731.91   $731.95   $731.90