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	$149.60	5.819%	$158.3052	$158.31	$158.30	$158.30
Purchase #2	$199.54	10.170%	$219.8332	$219.83	$219.85	$219.80
Purchase #3	$86.79	6.842%	$92.7282	$92.73	$92.75	$92.70
Purchase #4	$207.38	6.644%	$221.1583	$221.16	$221.15	$221.20
Purchase #5	$96.76	10.847%	$107.2556	$107.26	$107.25	$107.30
Purchase #6	$42.98	6.578%	$45.8072	$45.81	$45.80	$45.80
Purchase #7	$125.61	4.643%	$131.4421	$131.44	$131.45	$131.40
7 purchase totals =	$908.66		$976.5298	$976.54	$976.55	$976.50