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 $237.33   3.686%   $246.078   $246.08   $246.10   $246.10  
  Purchase #2 $93.70   6.154%   $99.4663   $99.47   $99.45   $99.50  
  Purchase #3 $91.73   4.675%   $96.0184   $96.02   $96.00   $96.00  
  Purchase #4 $73.51   11.826%   $82.2033   $82.20   $82.20   $82.20  
  Purchase #5 $226.63   8.380%   $245.6216   $245.62   $245.60   $245.60  
  Purchase #6 $242.85   10.309%   $267.8854   $267.89   $267.90   $267.90  
  Purchase #7 $212.98   7.483%   $228.9173   $228.92   $228.90   $228.90  
  7 purchase totals = $1,178.73       $1,266.1903   $1,266.20   $1,266.15   $1,266.20