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	$155.25	6.218%	$164.9034	$164.90	$164.90	$164.90
Purchase #2	$221.25	9.120%	$241.428	$241.43	$241.45	$241.40
Purchase #3	$220.68	4.812%	$231.2991	$231.30	$231.30	$231.30
Purchase #4	$179.41	3.520%	$185.7252	$185.73	$185.75	$185.70
Purchase #5	$161.32	4.212%	$168.1148	$168.11	$168.10	$168.10
Purchase #6	$197.89	12.475%	$222.5768	$222.58	$222.60	$222.60
Purchase #7	$187.91	12.532%	$211.4589	$211.46	$211.45	$211.50
7 purchase totals =	$1,323.71		$1,425.5062	$1,425.51	$1,425.55	$1,425.50