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 $72.32   4.551%   $75.6113   $75.61   $75.60   $75.60  
  Purchase #2 $216.47   8.483%   $234.8332   $234.83   $234.85   $234.80  
  Purchase #3 $72.62   6.323%   $77.2118   $77.21   $77.20   $77.20  
  Purchase #4 $197.81   3.526%   $204.7848   $204.78   $204.80   $204.80  
  Purchase #5 $123.64   3.416%   $127.8635   $127.86   $127.85   $127.90  
  Purchase #6 $68.69   8.658%   $74.6372   $74.64   $74.65   $74.60  
  Purchase #7 $15.39   12.650%   $17.3368   $17.34   $17.35   $17.30  
  7 purchase totals = $766.94       $812.2786   $812.27   $812.30   $812.20