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	$66.57	9.728%	$73.0459	$73.05	$73.05	$73.00
Purchase #2	$157.26	3.361%	$162.5455	$162.55	$162.55	$162.50
Purchase #3	$89.96	11.142%	$99.9833	$99.98	$100.00	$100.00
Purchase #4	$70.50	3.837%	$73.2051	$73.21	$73.20	$73.20
Purchase #5	$96.89	3.571%	$100.3499	$100.35	$100.35	$100.30
Purchase #6	$175.42	6.501%	$186.8241	$186.82	$186.80	$186.80
Purchase #7	$126.71	5.467%	$133.6372	$133.64	$133.65	$133.60
7 purchase totals =	$783.31		$829.5910	$829.60	$829.60	$829.40