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 $219.95   11.663%   $245.6028   $245.60   $245.60   $245.60  
  Purchase #2 $28.99   4.688%   $30.3491   $30.35   $30.35   $30.30  
  Purchase #3 $39.55   10.605%   $43.7443   $43.74   $43.75   $43.70  
  Purchase #4 $150.53   7.774%   $162.2322   $162.23   $162.25   $162.20  
  Purchase #5 $196.49   12.697%   $221.4383   $221.44   $221.45   $221.40  
  Purchase #6 $214.53   8.748%   $233.2971   $233.30   $233.30   $233.30  
  Purchase #7 $54.25   13.363%   $61.4994   $61.50   $61.50   $61.50  
  7 purchase totals = $904.29       $998.1632   $998.16   $998.20   $998.00