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	$121.71	12.488%	$136.9091	$136.91	$136.90	$136.90
Purchase #2	$202.55	12.713%	$228.3002	$228.30	$228.30	$228.30
Purchase #3	$107.66	9.662%	$118.0621	$118.06	$118.05	$118.10
Purchase #4	$160.30	7.557%	$172.4139	$172.41	$172.40	$172.40
Purchase #5	$226.65	3.204%	$233.9119	$233.91	$233.90	$233.90
Purchase #6	$179.92	5.199%	$189.274	$189.27	$189.25	$189.30
Purchase #7	$56.98	9.690%	$62.5014	$62.50	$62.50	$62.50
7 purchase totals =	$1,055.77		$1,141.3726	$1,141.36	$1,141.30	$1,141.40