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	$77.72	6.235%	$82.5658	$82.57	$82.55	$82.60
Purchase #2	$146.30	3.565%	$151.5156	$151.52	$151.50	$151.50
Purchase #3	$212.83	12.332%	$239.0762	$239.08	$239.10	$239.10
Purchase #4	$69.92	4.626%	$73.1545	$73.15	$73.15	$73.20
Purchase #5	$90.52	12.433%	$101.7744	$101.77	$101.75	$101.80
Purchase #6	$48.62	3.513%	$50.328	$50.33	$50.35	$50.30
Purchase #7	$247.98	4.570%	$259.3127	$259.31	$259.30	$259.30
7 purchase totals =	$893.89		$957.7272	$957.73	$957.70	$957.80