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	$40.75	12.856%	$45.9888	$45.99	$46.00	$46.00
Purchase #2	$155.98	7.316%	$167.3915	$167.39	$167.40	$167.40
Purchase #3	$100.76	7.627%	$108.445	$108.45	$108.45	$108.40
Purchase #4	$61.89	5.798%	$65.4784	$65.48	$65.50	$65.50
Purchase #5	$88.53	12.104%	$99.2457	$99.25	$99.25	$99.20
Purchase #6	$145.38	6.873%	$155.372	$155.37	$155.35	$155.40
Purchase #7	$244.75	10.436%	$270.2921	$270.29	$270.30	$270.30
7 purchase totals =	$838.04		$912.2135	$912.22	$912.25	$912.20