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 $223.72   10.239%   $246.6267   $246.63   $246.65   $246.60  
  Purchase #2 $61.44   12.760%   $69.2797   $69.28   $69.30   $69.30  
  Purchase #3 $175.66   12.710%   $197.9864   $197.99   $198.00   $198.00  
  Purchase #4 $127.44   9.545%   $139.6041   $139.60   $139.60   $139.60  
  Purchase #5 $58.76   11.175%   $65.3264   $65.33   $65.35   $65.30  
  Purchase #6 $147.64   4.376%   $154.1007   $154.10   $154.10   $154.10  
  Purchase #7 $240.32   7.481%   $258.2983   $258.30   $258.30   $258.30  
  7 purchase totals = $1,034.98       $1,131.2223   $1,131.23   $1,131.30   $1,131.20