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 $179.44   9.584%   $196.6375   $196.64   $196.65   $196.60  
  Purchase #2 $68.99   10.158%   $75.998   $76.00   $76.00   $76.00  
  Purchase #3 $64.89   9.545%   $71.0838   $71.08   $71.10   $71.10  
  Purchase #4 $103.54   3.291%   $106.9475   $106.95   $106.95   $106.90  
  Purchase #5 $232.33   4.796%   $243.4725   $243.47   $243.45   $243.50  
  Purchase #6 $217.46   8.601%   $236.1637   $236.16   $236.15   $236.20  
  Purchase #7 $233.70   6.498%   $248.8858   $248.89   $248.90   $248.90  
  7 purchase totals = $1,100.35       $1,179.1888   $1,179.19   $1,179.20   $1,179.20