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	$49.85	5.237%	$52.4606	$52.46	$52.45	$52.50
Purchase #2	$159.87	12.314%	$179.5564	$179.56	$179.55	$179.60
Purchase #3	$149.93	7.128%	$160.617	$160.62	$160.60	$160.60
Purchase #4	$245.52	4.359%	$256.2222	$256.22	$256.20	$256.20
Purchase #5	$139.59	7.830%	$150.5199	$150.52	$150.50	$150.50
Purchase #6	$207.46	4.304%	$216.3891	$216.39	$216.40	$216.40
Purchase #7	$25.61	3.343%	$26.4661	$26.47	$26.45	$26.50
7 purchase totals =	$977.83		$1,042.2313	$1,042.24	$1,042.15	$1,042.30