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	$72.97	10.182%	$80.3998	$80.40	$80.40	$80.40
Purchase #2	$113.88	11.806%	$127.3247	$127.32	$127.30	$127.30
Purchase #3	$44.34	4.351%	$46.2692	$46.27	$46.25	$46.30
Purchase #4	$80.58	10.618%	$89.136	$89.14	$89.15	$89.10
Purchase #5	$228.37	6.741%	$243.7644	$243.76	$243.75	$243.80
Purchase #6	$200.37	11.510%	$223.4326	$223.43	$223.45	$223.40
Purchase #7	$238.58	8.554%	$258.9881	$258.99	$259.00	$259.00
7 purchase totals =	$979.09		$1,069.3148	$1,069.31	$1,069.30	$1,069.30