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 $81.97   5.612%   $86.5702   $86.57   $86.55   $86.60  
  Purchase #2 $87.45   12.709%   $98.564   $98.56   $98.55   $98.60  
  Purchase #3 $180.81   8.273%   $195.7684   $195.77   $195.75   $195.80  
  Purchase #4 $111.70   13.593%   $126.8834   $126.88   $126.90   $126.90  
  Purchase #5 $231.88   9.625%   $254.1985   $254.20   $254.20   $254.20  
  Purchase #6 $196.44   7.566%   $211.3027   $211.30   $211.30   $211.30  
  Purchase #7 $233.73   4.421%   $244.0632   $244.06   $244.05   $244.10  
  7 purchase totals = $1,123.98       $1,217.3504   $1,217.34   $1,217.30   $1,217.50