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	$54.45	9.854%	$59.8155	$59.82	$59.80	$59.80
Purchase #2	$123.84	3.873%	$128.6363	$128.64	$128.65	$128.60
Purchase #3	$63.71	4.399%	$66.5126	$66.51	$66.50	$66.50
Purchase #4	$86.68	11.366%	$96.532	$96.53	$96.55	$96.50
Purchase #5	$41.89	3.780%	$43.4734	$43.47	$43.45	$43.50
Purchase #6	$242.41	6.775%	$258.8333	$258.83	$258.85	$258.80
Purchase #7	$120.41	6.123%	$127.7827	$127.78	$127.80	$127.80
7 purchase totals =	$733.39		$781.5858	$781.58	$781.60	$781.50