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	$109.57	9.103%	$119.5442	$119.54	$119.55	$119.50
Purchase #2	$38.92	6.377%	$41.4019	$41.40	$41.40	$41.40
Purchase #3	$25.78	5.812%	$27.2783	$27.28	$27.30	$27.30
Purchase #4	$86.36	4.139%	$89.9344	$89.93	$89.95	$89.90
Purchase #5	$207.89	7.204%	$222.8664	$222.87	$222.85	$222.90
Purchase #6	$180.39	11.267%	$200.7145	$200.71	$200.70	$200.70
Purchase #7	$145.37	5.413%	$153.2389	$153.24	$153.25	$153.20
7 purchase totals =	$794.28		$854.9786	$854.97	$855.00	$854.90