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	$85.31	4.495%	$89.1447	$89.14	$89.15	$89.10
Purchase #2	$234.40	10.805%	$259.7269	$259.73	$259.75	$259.70
Purchase #3	$154.76	12.137%	$173.5432	$173.54	$173.55	$173.50
Purchase #4	$208.99	12.104%	$234.2861	$234.29	$234.30	$234.30
Purchase #5	$27.83	3.789%	$28.8845	$28.88	$28.90	$28.90
Purchase #6	$81.46	12.844%	$91.9227	$91.92	$91.90	$91.90
Purchase #7	$103.96	5.243%	$109.4106	$109.41	$109.40	$109.40
7 purchase totals =	$896.71		$986.9187	$986.91	$986.95	$986.80