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 $216.55   13.638%   $246.0831   $246.08   $246.10   $246.10  
  Purchase #2 $175.36   9.808%   $192.5593   $192.56   $192.55   $192.60  
  Purchase #3 $185.93   10.802%   $206.0142   $206.01   $206.00   $206.00  
  Purchase #4 $25.99   13.856%   $29.5912   $29.59   $29.60   $29.60  
  Purchase #5 $106.90   11.300%   $118.9797   $118.98   $119.00   $119.00  
  Purchase #6 $212.85   5.291%   $224.1119   $224.11   $224.10   $224.10  
  Purchase #7 $204.45   11.493%   $227.9474   $227.95   $227.95   $227.90  
  7 purchase totals = $1,128.03       $1,245.2868   $1,245.28   $1,245.30   $1,245.30