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	$69.85	12.753%	$78.758	$78.76	$78.75	$78.80
Purchase #2	$145.61	11.652%	$162.5765	$162.58	$162.60	$162.60
Purchase #3	$43.83	5.417%	$46.2043	$46.20	$46.20	$46.20
Purchase #4	$39.63	3.228%	$40.9093	$40.91	$40.90	$40.90
Purchase #5	$102.58	8.820%	$111.6276	$111.63	$111.65	$111.60
Purchase #6	$114.40	12.359%	$128.5387	$128.54	$128.55	$128.50
Purchase #7	$73.37	8.571%	$79.6585	$79.66	$79.65	$79.70
7 purchase totals =	$589.27		$648.2729	$648.28	$648.30	$648.30