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 $218.51   8.122%   $236.2574   $236.26   $236.25   $236.30  
  Purchase #2 $73.60   3.280%   $76.0141   $76.01   $76.00   $76.00  
  Purchase #3 $26.92   9.338%   $29.4338   $29.43   $29.45   $29.40  
  Purchase #4 $99.57   8.364%   $107.898   $107.90   $107.90   $107.90  
  Purchase #5 $192.28   5.680%   $203.2015   $203.20   $203.20   $203.20  
  Purchase #6 $216.28   13.409%   $245.281   $245.28   $245.30   $245.30  
  Purchase #7 $20.29   3.591%   $21.0186   $21.02   $21.00   $21.00  
  7 purchase totals = $847.45       $919.1044   $919.10   $919.10   $919.10