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	$177.83	12.644%	$200.3148	$200.31	$200.30	$200.30
Purchase #2	$97.98	13.717%	$111.4199	$111.42	$111.40	$111.40
Purchase #3	$73.58	3.104%	$75.8639	$75.86	$75.85	$75.90
Purchase #4	$225.53	6.421%	$240.0113	$240.01	$240.00	$240.00
Purchase #5	$226.38	12.296%	$254.2157	$254.22	$254.20	$254.20
Purchase #6	$49.37	13.280%	$55.9263	$55.93	$55.95	$55.90
Purchase #7	$180.72	5.329%	$190.3506	$190.35	$190.35	$190.40
7 purchase totals =	$1,031.39		$1,128.1025	$1,128.10	$1,128.05	$1,128.10