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 $153.45   7.199%   $164.4969   $164.50   $164.50   $164.50  
  Purchase #2 $246.63   8.235%   $266.94   $266.94   $266.95   $266.90  
  Purchase #3 $44.96   11.343%   $50.0598   $50.06   $50.05   $50.10  
  Purchase #4 $71.85   10.675%   $79.52   $79.52   $79.50   $79.50  
  Purchase #5 $67.35   7.864%   $72.6464   $72.65   $72.65   $72.60  
  Purchase #6 $17.38   10.497%   $19.2044   $19.20   $19.20   $19.20  
  Purchase #7 $123.53   8.126%   $133.568   $133.57   $133.55   $133.60  
  7 purchase totals = $725.15       $786.4355   $786.44   $786.40   $786.40