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	$34.56	9.454%	$37.8273	$37.83	$37.85	$37.80
Purchase #2	$220.75	4.419%	$230.5049	$230.50	$230.50	$230.50
Purchase #3	$16.66	11.190%	$18.5243	$18.52	$18.50	$18.50
Purchase #4	$133.80	6.358%	$142.307	$142.31	$142.30	$142.30
Purchase #5	$65.42	4.769%	$68.5399	$68.54	$68.55	$68.50
Purchase #6	$69.47	7.415%	$74.6212	$74.62	$74.60	$74.60
Purchase #7	$180.31	11.413%	$200.8888	$200.89	$200.90	$200.90
7 purchase totals =	$720.97		$773.2134	$773.21	$773.20	$773.10