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	$238.62	13.848%	$271.6641	$271.66	$271.65	$271.70
Purchase #2	$53.33	11.209%	$59.3078	$59.31	$59.30	$59.30
Purchase #3	$132.32	8.241%	$143.2245	$143.22	$143.20	$143.20
Purchase #4	$129.70	13.555%	$147.2808	$147.28	$147.30	$147.30
Purchase #5	$215.69	10.557%	$238.4604	$238.46	$238.45	$238.50
Purchase #6	$8.50	4.859%	$8.913	$8.91	$8.90	$8.90
Purchase #7	$245.97	5.306%	$259.0212	$259.02	$259.00	$259.00
7 purchase totals =	$1,024.13		$1,127.8718	$1,127.86	$1,127.80	$1,127.90