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	$48.50	12.667%	$54.6435	$54.64	$54.65	$54.60
Purchase #2	$38.32	6.837%	$40.9399	$40.94	$40.95	$40.90
Purchase #3	$75.43	9.145%	$82.3281	$82.33	$82.35	$82.30
Purchase #4	$203.74	5.729%	$215.4123	$215.41	$215.40	$215.40
Purchase #5	$36.71	4.593%	$38.3961	$38.40	$38.40	$38.40
Purchase #6	$34.78	6.865%	$37.1676	$37.17	$37.15	$37.20
Purchase #7	$41.27	5.504%	$43.5415	$43.54	$43.55	$43.50
7 purchase totals =	$478.75		$512.4290	$512.43	$512.45	$512.30