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 $127.44   13.335%   $144.4341   $144.43   $144.45   $144.40  
  Purchase #2 $203.42   6.447%   $216.5345   $216.53   $216.55   $216.50  
  Purchase #3 $88.43   8.557%   $95.997   $96.00   $96.00   $96.00  
  Purchase #4 $23.98   8.778%   $26.085   $26.09   $26.10   $26.10  
  Purchase #5 $19.94   10.169%   $21.9677   $21.97   $21.95   $22.00  
  Purchase #6 $230.73   6.868%   $246.5765   $246.58   $246.60   $246.60  
  Purchase #7 $247.91   7.289%   $265.9802   $265.98   $266.00   $266.00  
  7 purchase totals = $941.85       $1,017.5750   $1,017.58   $1,017.65   $1,017.60