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	$248.45	7.271%	$266.5148	$266.51	$266.50	$266.50
Purchase #2	$48.62	13.170%	$55.0233	$55.02	$55.00	$55.00
Purchase #3	$99.29	6.287%	$105.5324	$105.53	$105.55	$105.50
Purchase #4	$128.93	5.544%	$136.0779	$136.08	$136.10	$136.10
Purchase #5	$210.60	5.135%	$221.4143	$221.41	$221.40	$221.40
Purchase #6	$39.73	7.226%	$42.6009	$42.60	$42.60	$42.60
Purchase #7	$13.71	4.803%	$14.3685	$14.37	$14.35	$14.40
7 purchase totals =	$789.33		$841.5321	$841.52	$841.50	$841.50