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 $234.85   11.482%   $261.8155   $261.82   $261.80   $261.80  
  Purchase #2 $164.53   10.150%   $181.2298   $181.23   $181.25   $181.20  
  Purchase #3 $10.93   10.574%   $12.0857   $12.09   $12.10   $12.10  
  Purchase #4 $246.55   5.434%   $259.9475   $259.95   $259.95   $259.90  
  Purchase #5 $222.84   9.280%   $243.5196   $243.52   $243.50   $243.50  
  Purchase #6 $124.30   9.509%   $136.1197   $136.12   $136.10   $136.10  
  Purchase #7 $231.34   7.592%   $248.9033   $248.90   $248.90   $248.90  
  7 purchase totals = $1,235.34       $1,343.6211   $1,343.63   $1,343.60   $1,343.50