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	$113.59	7.127%	$121.6856	$121.69	$121.70	$121.70
Purchase #2	$97.83	3.104%	$100.8666	$100.87	$100.85	$100.90
Purchase #3	$170.98	13.531%	$194.1153	$194.12	$194.10	$194.10
Purchase #4	$233.98	4.746%	$245.0847	$245.08	$245.10	$245.10
Purchase #5	$100.26	3.652%	$103.9215	$103.92	$103.90	$103.90
Purchase #6	$231.46	5.706%	$244.6671	$244.67	$244.65	$244.70
Purchase #7	$67.93	6.606%	$72.4175	$72.42	$72.40	$72.40
7 purchase totals =	$1,016.03		$1,082.7583	$1,082.77	$1,082.70	$1,082.80