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	$79.99	4.792%	$83.8231	$83.82	$83.80	$83.80
Purchase #2	$94.63	5.135%	$99.4893	$99.49	$99.50	$99.50
Purchase #3	$222.56	12.426%	$250.2153	$250.22	$250.20	$250.20
Purchase #4	$28.65	12.201%	$32.1456	$32.15	$32.15	$32.10
Purchase #5	$205.88	8.721%	$223.8348	$223.83	$223.85	$223.80
Purchase #6	$152.75	12.463%	$171.7872	$171.79	$171.80	$171.80
Purchase #7	$176.31	5.228%	$185.5275	$185.53	$185.55	$185.50
7 purchase totals =	$960.77		$1,046.8228	$1,046.83	$1,046.85	$1,046.70