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	$233.26	9.111%	$254.5123	$254.51	$254.50	$254.50
Purchase #2	$123.93	12.608%	$139.5551	$139.56	$139.55	$139.60
Purchase #3	$79.77	12.376%	$89.6423	$89.64	$89.65	$89.60
Purchase #4	$35.51	8.624%	$38.5724	$38.57	$38.55	$38.60
Purchase #5	$120.98	5.515%	$127.652	$127.65	$127.65	$127.70
Purchase #6	$145.90	4.379%	$152.289	$152.29	$152.30	$152.30
Purchase #7	$180.38	6.778%	$192.6062	$192.61	$192.60	$192.60
7 purchase totals =	$919.73		$994.8293	$994.83	$994.80	$994.90