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 $83.45   6.644%   $88.9944   $88.99   $89.00   $89.00  
  Purchase #2 $98.69   4.677%   $103.3057   $103.31   $103.30   $103.30  
  Purchase #3 $48.76   6.259%   $51.8119   $51.81   $51.80   $51.80  
  Purchase #4 $225.53   8.704%   $245.1601   $245.16   $245.15   $245.20  
  Purchase #5 $169.51   6.536%   $180.5892   $180.59   $180.60   $180.60  
  Purchase #6 $177.73   8.695%   $193.1836   $193.18   $193.20   $193.20  
  Purchase #7 $193.85   5.684%   $204.8684   $204.87   $204.85   $204.90  
  7 purchase totals = $997.52       $1,067.9133   $1,067.91   $1,067.90   $1,068.00