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	$48.78	12.360%	$54.8092	$54.81	$54.80	$54.80
Purchase #2	$178.90	8.432%	$193.9848	$193.98	$194.00	$194.00
Purchase #3	$187.27	6.675%	$199.7703	$199.77	$199.75	$199.80
Purchase #4	$212.92	13.380%	$241.4087	$241.41	$241.40	$241.40
Purchase #5	$16.26	12.756%	$18.3341	$18.33	$18.35	$18.30
Purchase #6	$172.61	7.337%	$185.2744	$185.27	$185.25	$185.30
Purchase #7	$91.77	9.159%	$100.1752	$100.18	$100.20	$100.20
7 purchase totals =	$908.51		$993.7567	$993.75	$993.75	$993.80