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	$107.42	3.474%	$111.1518	$111.15	$111.15	$111.20
Purchase #2	$39.28	4.838%	$41.1804	$41.18	$41.20	$41.20
Purchase #3	$136.33	4.223%	$142.0872	$142.09	$142.10	$142.10
Purchase #4	$29.31	10.789%	$32.4723	$32.47	$32.45	$32.50
Purchase #5	$195.27	4.399%	$203.8599	$203.86	$203.85	$203.90
Purchase #6	$57.79	4.807%	$60.568	$60.57	$60.55	$60.60
Purchase #7	$29.76	10.451%	$32.8702	$32.87	$32.85	$32.90
7 purchase totals =	$595.16		$624.1898	$624.19	$624.15	$624.40