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	$156.65	9.745%	$171.9155	$171.92	$171.90	$171.90
Purchase #2	$147.52	7.254%	$158.2211	$158.22	$158.20	$158.20
Purchase #3	$170.84	9.758%	$187.5106	$187.51	$187.50	$187.50
Purchase #4	$32.84	6.471%	$34.9651	$34.97	$34.95	$35.00
Purchase #5	$100.45	12.607%	$113.1137	$113.11	$113.10	$113.10
Purchase #6	$241.42	5.349%	$254.3336	$254.33	$254.35	$254.30
Purchase #7	$92.98	5.646%	$98.2297	$98.23	$98.25	$98.20
7 purchase totals =	$942.70		$1,018.2893	$1,018.29	$1,018.25	$1,018.20