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	$135.50	6.845%	$144.775	$144.78	$144.80	$144.80
Purchase #2	$77.65	4.828%	$81.3989	$81.40	$81.40	$81.40
Purchase #3	$209.63	9.285%	$229.0941	$229.09	$229.10	$229.10
Purchase #4	$88.74	12.332%	$99.6834	$99.68	$99.70	$99.70
Purchase #5	$36.53	11.763%	$40.827	$40.83	$40.85	$40.80
Purchase #6	$178.37	4.764%	$186.8675	$186.87	$186.85	$186.90
Purchase #7	$76.89	7.523%	$82.6744	$82.67	$82.65	$82.70
7 purchase totals =	$803.31		$865.3203	$865.32	$865.35	$865.40