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	$31.49	13.300%	$35.6782	$35.68	$35.70	$35.70
Purchase #2	$136.76	4.625%	$143.0852	$143.09	$143.10	$143.10
Purchase #3	$176.33	13.686%	$200.4625	$200.46	$200.45	$200.50
Purchase #4	$69.87	4.218%	$72.8171	$72.82	$72.80	$72.80
Purchase #5	$46.56	10.711%	$51.547	$51.55	$51.55	$51.50
Purchase #6	$210.26	13.346%	$238.3213	$238.32	$238.30	$238.30
Purchase #7	$174.92	3.342%	$180.7658	$180.77	$180.75	$180.80
7 purchase totals =	$846.19		$922.6771	$922.69	$922.65	$922.70