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 $80.30   4.677%   $84.0556   $84.06   $84.05   $84.10  
  Purchase #2 $223.41   13.393%   $253.3313   $253.33   $253.35   $253.30  
  Purchase #3 $241.61   13.524%   $274.2853   $274.29   $274.30   $274.30  
  Purchase #4 $96.77   13.347%   $109.6859   $109.69   $109.70   $109.70  
  Purchase #5 $122.43   3.636%   $126.8816   $126.88   $126.90   $126.90  
  Purchase #6 $69.53   11.307%   $77.3918   $77.39   $77.40   $77.40  
  Purchase #7 $178.61   5.304%   $188.0835   $188.08   $188.10   $188.10  
  7 purchase totals = $1,012.66       $1,113.7150   $1,113.72   $1,113.80   $1,113.80