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	$192.25	7.424%	$206.5226	$206.52	$206.50	$206.50
Purchase #2	$155.63	6.615%	$165.9249	$165.92	$165.90	$165.90
Purchase #3	$160.41	13.352%	$181.8279	$181.83	$181.85	$181.80
Purchase #4	$77.76	5.228%	$81.8253	$81.83	$81.85	$81.80
Purchase #5	$51.89	5.842%	$54.9214	$54.92	$54.90	$54.90
Purchase #6	$41.81	3.395%	$43.2294	$43.23	$43.25	$43.20
Purchase #7	$34.39	6.231%	$36.5328	$36.53	$36.55	$36.50
7 purchase totals =	$714.14		$770.7843	$770.78	$770.80	$770.60