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 $86.46   13.611%   $98.2281   $98.23   $98.25   $98.20  
  Purchase #2 $154.36   3.469%   $159.7147   $159.71   $159.70   $159.70  
  Purchase #3 $243.25   9.417%   $266.1569   $266.16   $266.15   $266.20  
  Purchase #4 $5.87   7.602%   $6.3162   $6.32   $6.30   $6.30  
  Purchase #5 $174.45   7.714%   $187.9071   $187.91   $187.90   $187.90  
  Purchase #6 $153.62   13.275%   $174.0131   $174.01   $174.00   $174.00  
  Purchase #7 $104.74   6.273%   $111.3103   $111.31   $111.30   $111.30  
  7 purchase totals = $922.75       $1,003.6464   $1,003.65   $1,003.60   $1,003.60