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	$180.46	13.335%	$204.5243	$204.52	$204.50	$204.50
Purchase #2	$55.52	4.171%	$57.8357	$57.84	$57.85	$57.80
Purchase #3	$31.46	12.166%	$35.2874	$35.29	$35.30	$35.30
Purchase #4	$109.65	3.301%	$113.2695	$113.27	$113.25	$113.30
Purchase #5	$199.27	6.837%	$212.8941	$212.89	$212.90	$212.90
Purchase #6	$39.67	12.822%	$44.7565	$44.76	$44.75	$44.80
Purchase #7	$239.96	10.552%	$265.2806	$265.28	$265.30	$265.30
7 purchase totals =	$855.99		$933.8481	$933.85	$933.85	$933.90