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	$216.99	13.128%	$245.4764	$245.48	$245.50	$245.50
Purchase #2	$96.71	12.860%	$109.1469	$109.15	$109.15	$109.10
Purchase #3	$123.76	8.557%	$134.3501	$134.35	$134.35	$134.40
Purchase #4	$150.25	4.414%	$156.882	$156.88	$156.90	$156.90
Purchase #5	$209.91	10.163%	$231.2432	$231.24	$231.25	$231.20
Purchase #6	$185.52	10.780%	$205.5191	$205.52	$205.50	$205.50
Purchase #7	$134.52	4.403%	$140.4429	$140.44	$140.45	$140.40
7 purchase totals =	$1,117.66		$1,223.0606	$1,223.06	$1,223.10	$1,223.00