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 $167.81   10.642%   $185.6683   $185.67   $185.65   $185.70  
  Purchase #2 $234.87   10.569%   $259.6934   $259.69   $259.70   $259.70  
  Purchase #3 $11.96   5.486%   $12.6161   $12.62   $12.60   $12.60  
  Purchase #4 $44.81   7.547%   $48.1918   $48.19   $48.20   $48.20  
  Purchase #5 $235.95   12.872%   $266.3215   $266.32   $266.30   $266.30  
  Purchase #6 $248.54   3.714%   $257.7708   $257.77   $257.75   $257.80  
  Purchase #7 $44.39   5.184%   $46.6912   $46.69   $46.70   $46.70  
  7 purchase totals = $988.33       $1,076.9531   $1,076.95   $1,076.90   $1,077.00