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	$111.54	8.609%	$121.1425	$121.14	$121.15	$121.10
Purchase #2	$126.87	8.373%	$137.4928	$137.49	$137.50	$137.50
Purchase #3	$168.45	6.151%	$178.8114	$178.81	$178.80	$178.80
Purchase #4	$231.60	9.845%	$254.401	$254.40	$254.40	$254.40
Purchase #5	$169.66	10.210%	$186.9823	$186.98	$187.00	$187.00
Purchase #6	$84.58	6.319%	$89.9246	$89.92	$89.90	$89.90
Purchase #7	$29.91	11.268%	$33.2803	$33.28	$33.30	$33.30
7 purchase totals =	$922.61		$1,002.0349	$1,002.02	$1,002.05	$1,002.00