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 $5.33   11.458%   $5.9407   $5.94   $5.95   $5.90  
  Purchase #2 $206.86   9.720%   $226.9668   $226.97   $226.95   $227.00  
  Purchase #3 $61.32   8.560%   $66.569   $66.57   $66.55   $66.60  
  Purchase #4 $225.77   11.708%   $252.2032   $252.20   $252.20   $252.20  
  Purchase #5 $97.34   4.129%   $101.3592   $101.36   $101.35   $101.40  
  Purchase #6 $118.91   4.206%   $123.9114   $123.91   $123.90   $123.90  
  Purchase #7 $182.60   7.506%   $196.306   $196.31   $196.30   $196.30  
  7 purchase totals = $898.13       $973.2563   $973.26   $973.20   $973.30