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 $246.65   6.710%   $263.2002   $263.20   $263.20   $263.20  
  Purchase #2 $35.44   12.852%   $39.9947   $39.99   $40.00   $40.00  
  Purchase #3 $227.34   5.835%   $240.6053   $240.61   $240.60   $240.60  
  Purchase #4 $225.83   13.352%   $255.9828   $255.98   $256.00   $256.00  
  Purchase #5 $193.99   7.355%   $208.258   $208.26   $208.25   $208.30  
  Purchase #6 $49.33   10.121%   $54.3227   $54.32   $54.30   $54.30  
  Purchase #7 $138.62   3.664%   $143.699   $143.70   $143.70   $143.70  
  7 purchase totals = $1,117.20       $1,206.0627   $1,206.06   $1,206.05   $1,206.10