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	$52.83	4.359%	$55.1329	$55.13	$55.15	$55.10
Purchase #2	$167.78	4.602%	$175.5012	$175.50	$175.50	$175.50
Purchase #3	$15.59	7.104%	$16.6975	$16.70	$16.70	$16.70
Purchase #4	$200.31	10.212%	$220.7657	$220.77	$220.75	$220.80
Purchase #5	$129.69	7.479%	$139.3895	$139.39	$139.40	$139.40
Purchase #6	$78.33	13.478%	$88.8873	$88.89	$88.90	$88.90
Purchase #7	$121.92	4.457%	$127.354	$127.35	$127.35	$127.40
7 purchase totals =	$766.45		$823.7281	$823.73	$823.75	$823.80