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 $58.94   4.348%   $61.5027   $61.50   $61.50   $61.50  
  Purchase #2 $143.63   8.830%   $156.3125   $156.31   $156.30   $156.30  
  Purchase #3 $165.61   10.465%   $182.9411   $182.94   $182.95   $182.90  
  Purchase #4 $240.33   12.680%   $270.8038   $270.80   $270.80   $270.80  
  Purchase #5 $68.73   4.829%   $72.049   $72.05   $72.05   $72.00  
  Purchase #6 $181.99   6.246%   $193.3571   $193.36   $193.35   $193.40  
  Purchase #7 $9.37   7.456%   $10.0686   $10.07   $10.05   $10.10  
  7 purchase totals = $868.60       $947.0348   $947.03   $947.00   $947.00