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	$45.74	6.699%	$48.8041	$48.80	$48.80	$48.80
Purchase #2	$38.68	12.517%	$43.5216	$43.52	$43.50	$43.50
Purchase #3	$211.65	5.139%	$222.5267	$222.53	$222.55	$222.50
Purchase #4	$166.82	5.294%	$175.6515	$175.65	$175.65	$175.70
Purchase #5	$104.73	7.191%	$112.2611	$112.26	$112.25	$112.30
Purchase #6	$133.63	5.746%	$141.3084	$141.31	$141.30	$141.30
Purchase #7	$32.42	9.263%	$35.4231	$35.42	$35.40	$35.40
7 purchase totals =	$733.67		$779.4965	$779.49	$779.45	$779.50