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	$28.89	5.684%	$30.5321	$30.53	$30.55	$30.50
Purchase #2	$94.57	11.583%	$105.524	$105.52	$105.50	$105.50
Purchase #3	$126.87	11.349%	$141.2685	$141.27	$141.25	$141.30
Purchase #4	$149.66	6.339%	$159.1469	$159.15	$159.15	$159.10
Purchase #5	$124.50	13.481%	$141.2838	$141.28	$141.30	$141.30
Purchase #6	$222.39	12.627%	$250.4712	$250.47	$250.45	$250.50
Purchase #7	$71.46	5.600%	$75.4618	$75.46	$75.45	$75.50
7 purchase totals =	$818.34		$903.6883	$903.68	$903.65	$903.70