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	$9.54	6.256%	$10.1368	$10.14	$10.15	$10.10
Purchase #2	$170.30	3.769%	$176.7186	$176.72	$176.70	$176.70
Purchase #3	$141.35	13.818%	$160.8817	$160.88	$160.90	$160.90
Purchase #4	$188.95	10.851%	$209.453	$209.45	$209.45	$209.50
Purchase #5	$170.57	5.580%	$180.0878	$180.09	$180.10	$180.10
Purchase #6	$129.59	12.783%	$146.1555	$146.16	$146.15	$146.20
Purchase #7	$202.70	12.712%	$228.4672	$228.47	$228.45	$228.50
7 purchase totals =	$1,013.00		$1,111.9006	$1,111.91	$1,111.90	$1,112.00