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	$157.25	8.790%	$171.0723	$171.07	$171.05	$171.10
Purchase #2	$152.78	13.179%	$172.9149	$172.91	$172.90	$172.90
Purchase #3	$133.59	8.135%	$144.4575	$144.46	$144.45	$144.50
Purchase #4	$26.72	13.353%	$30.2879	$30.29	$30.30	$30.30
Purchase #5	$97.33	9.390%	$106.4693	$106.47	$106.45	$106.50
Purchase #6	$46.97	6.223%	$49.8929	$49.89	$49.90	$49.90
Purchase #7	$85.61	10.487%	$94.5879	$94.59	$94.60	$94.60
7 purchase totals =	$700.25		$769.6827	$769.68	$769.65	$769.80