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	$49.88	3.346%	$51.549	$51.55	$51.55	$51.50
Purchase #2	$49.46	13.486%	$56.1302	$56.13	$56.15	$56.10
Purchase #3	$198.82	12.405%	$223.4836	$223.48	$223.50	$223.50
Purchase #4	$138.83	4.657%	$145.2953	$145.30	$145.30	$145.30
Purchase #5	$110.72	9.154%	$120.8553	$120.86	$120.85	$120.90
Purchase #6	$63.64	6.585%	$67.8307	$67.83	$67.85	$67.80
Purchase #7	$73.43	8.178%	$79.4351	$79.44	$79.45	$79.40
7 purchase totals =	$684.78		$744.5792	$744.59	$744.65	$744.50