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	$47.40	7.212%	$50.8185	$50.82	$50.80	$50.80
Purchase #2	$242.62	13.129%	$274.4736	$274.47	$274.45	$274.50
Purchase #3	$118.86	6.855%	$127.0079	$127.01	$127.00	$127.00
Purchase #4	$133.68	8.761%	$145.3917	$145.39	$145.40	$145.40
Purchase #5	$41.71	12.705%	$47.0093	$47.01	$47.00	$47.00
Purchase #6	$83.96	9.233%	$91.712	$91.71	$91.70	$91.70
Purchase #7	$118.50	8.278%	$128.3094	$128.31	$128.30	$128.30
7 purchase totals =	$786.73		$864.7224	$864.72	$864.65	$864.70