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	$198.42	11.588%	$221.4129	$221.41	$221.40	$221.40
Purchase #2	$212.46	11.466%	$236.8207	$236.82	$236.80	$236.80
Purchase #3	$118.52	10.534%	$131.0049	$131.00	$131.00	$131.00
Purchase #4	$62.62	6.645%	$66.7811	$66.78	$66.80	$66.80
Purchase #5	$96.35	5.250%	$101.4084	$101.41	$101.40	$101.40
Purchase #6	$213.90	9.273%	$233.7349	$233.73	$233.75	$233.70
Purchase #7	$11.45	11.528%	$12.77	$12.77	$12.75	$12.80
7 purchase totals =	$913.72		$1,003.9329	$1,003.92	$1,003.90	$1,003.90