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	$189.55	5.468%	$199.9146	$199.91	$199.90	$199.90
Purchase #2	$127.59	9.308%	$139.4661	$139.47	$139.45	$139.50
Purchase #3	$124.81	7.122%	$133.699	$133.70	$133.70	$133.70
Purchase #4	$183.31	9.533%	$200.7849	$200.78	$200.80	$200.80
Purchase #5	$89.75	11.860%	$100.3944	$100.39	$100.40	$100.40
Purchase #6	$75.28	13.462%	$85.4142	$85.41	$85.40	$85.40
Purchase #7	$127.98	3.223%	$132.1048	$132.10	$132.10	$132.10
7 purchase totals =	$918.27		$991.7780	$991.76	$991.75	$991.80