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 $65.63   5.251%   $69.0762   $69.08   $69.10   $69.10  
  Purchase #2 $93.60   10.744%   $103.6564   $103.66   $103.65   $103.70  
  Purchase #3 $34.52   12.620%   $38.8764   $38.88   $38.90   $38.90  
  Purchase #4 $166.53   12.706%   $187.6893   $187.69   $187.70   $187.70  
  Purchase #5 $211.54   7.558%   $227.5282   $227.53   $227.55   $227.50  
  Purchase #6 $180.34   10.463%   $199.209   $199.21   $199.20   $199.20  
  Purchase #7 $124.38   4.254%   $129.6711   $129.67   $129.65   $129.70  
  7 purchase totals = $876.54       $955.7066   $955.72   $955.75   $955.80