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	$227.53	12.180%	$255.2432	$255.24	$255.25	$255.20
Purchase #2	$151.90	12.697%	$171.1867	$171.19	$171.20	$171.20
Purchase #3	$228.74	11.446%	$254.9216	$254.92	$254.90	$254.90
Purchase #4	$32.48	8.529%	$35.2502	$35.25	$35.25	$35.30
Purchase #5	$77.27	10.500%	$85.3834	$85.38	$85.40	$85.40
Purchase #6	$137.75	11.521%	$153.6202	$153.62	$153.60	$153.60
Purchase #7	$84.91	8.724%	$92.3175	$92.32	$92.30	$92.30
7 purchase totals =	$940.58		$1,047.9228	$1,047.92	$1,047.90	$1,047.90