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	$34.83	11.814%	$38.9448	$38.94	$38.95	$38.90
Purchase #2	$83.72	10.691%	$92.6705	$92.67	$92.65	$92.70
Purchase #3	$94.25	11.498%	$105.0869	$105.09	$105.10	$105.10
Purchase #4	$108.98	4.760%	$114.1674	$114.17	$114.15	$114.20
Purchase #5	$69.31	3.708%	$71.88	$71.88	$71.90	$71.90
Purchase #6	$38.96	12.477%	$43.821	$43.82	$43.80	$43.80
Purchase #7	$151.55	13.653%	$172.2411	$172.24	$172.25	$172.20
7 purchase totals =	$581.60		$638.8117	$638.81	$638.80	$638.80