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	$25.27	7.121%	$27.0695	$27.07	$27.05	$27.10
Purchase #2	$88.71	13.305%	$100.5129	$100.51	$100.50	$100.50
Purchase #3	$89.33	4.856%	$93.6679	$93.67	$93.65	$93.70
Purchase #4	$82.42	12.280%	$92.5412	$92.54	$92.55	$92.50
Purchase #5	$55.67	3.511%	$57.6246	$57.62	$57.60	$57.60
Purchase #6	$100.49	9.546%	$110.0828	$110.08	$110.10	$110.10
Purchase #7	$88.87	11.367%	$98.9719	$98.97	$98.95	$99.00
7 purchase totals =	$530.76		$580.4708	$580.46	$580.40	$580.50