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	$25.87	5.114%	$27.193	$27.19	$27.20	$27.20
Purchase #2	$190.71	10.584%	$210.8947	$210.89	$210.90	$210.90
Purchase #3	$126.61	12.409%	$142.321	$142.32	$142.30	$142.30
Purchase #4	$42.29	8.259%	$45.7827	$45.78	$45.80	$45.80
Purchase #5	$57.40	9.683%	$62.958	$62.96	$62.95	$63.00
Purchase #6	$42.67	12.137%	$47.8489	$47.85	$47.85	$47.80
Purchase #7	$250.75	9.194%	$273.804	$273.80	$273.80	$273.80
7 purchase totals =	$736.30		$810.8023	$810.79	$810.80	$810.80