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	$202.99	3.630%	$210.3585	$210.36	$210.35	$210.40
Purchase #2	$230.85	6.564%	$246.003	$246.00	$246.00	$246.00
Purchase #3	$54.29	6.638%	$57.8938	$57.89	$57.90	$57.90
Purchase #4	$38.49	3.763%	$39.9384	$39.94	$39.95	$39.90
Purchase #5	$164.55	12.618%	$185.3129	$185.31	$185.30	$185.30
Purchase #6	$89.50	13.197%	$101.3113	$101.31	$101.30	$101.30
Purchase #7	$127.48	3.216%	$131.5798	$131.58	$131.60	$131.60
7 purchase totals =	$908.15		$972.3977	$972.39	$972.40	$972.40