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	$47.92	8.192%	$51.8456	$51.85	$51.85	$51.80
Purchase #2	$152.35	8.257%	$164.9295	$164.93	$164.95	$164.90
Purchase #3	$48.54	7.296%	$52.0815	$52.08	$52.10	$52.10
Purchase #4	$206.49	11.312%	$229.8481	$229.85	$229.85	$229.80
Purchase #5	$243.76	5.378%	$256.8694	$256.87	$256.85	$256.90
Purchase #6	$79.62	12.621%	$89.6688	$89.67	$89.65	$89.70
Purchase #7	$143.54	9.778%	$157.5753	$157.58	$157.60	$157.60
7 purchase totals =	$922.22		$1,002.8182	$1,002.83	$1,002.85	$1,002.80