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 $173.31   5.577%   $182.9755   $182.98   $183.00   $183.00  
  Purchase #2 $5.86   3.751%   $6.0798   $6.08   $6.10   $6.10  
  Purchase #3 $242.62   11.441%   $270.3782   $270.38   $270.40   $270.40  
  Purchase #4 $29.30   4.591%   $30.6452   $30.65   $30.65   $30.60  
  Purchase #5 $160.50   10.208%   $176.8838   $176.88   $176.90   $176.90  
  Purchase #6 $207.77   11.626%   $231.9253   $231.93   $231.95   $231.90  
  Purchase #7 $64.32   6.234%   $68.3297   $68.33   $68.35   $68.30  
  7 purchase totals = $883.68       $967.2175   $967.23   $967.35   $967.20