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	$225.35	3.523%	$233.2891	$233.29	$233.30	$233.30
Purchase #2	$77.38	3.778%	$80.3034	$80.30	$80.30	$80.30
Purchase #3	$79.61	8.633%	$86.4827	$86.48	$86.50	$86.50
Purchase #4	$156.83	13.647%	$178.2326	$178.23	$178.25	$178.20
Purchase #5	$236.60	8.468%	$256.6353	$256.64	$256.65	$256.60
Purchase #6	$135.53	6.579%	$144.4465	$144.45	$144.45	$144.40
Purchase #7	$20.98	8.624%	$22.7893	$22.79	$22.80	$22.80
7 purchase totals =	$932.28		$1,002.1789	$1,002.18	$1,002.25	$1,002.10