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	$38.78	11.160%	$43.1078	$43.11	$43.10	$43.10
Purchase #2	$176.74	12.614%	$199.034	$199.03	$199.05	$199.00
Purchase #3	$62.92	11.697%	$70.2798	$70.28	$70.30	$70.30
Purchase #4	$240.53	3.414%	$248.7417	$248.74	$248.75	$248.70
Purchase #5	$174.41	9.473%	$190.9319	$190.93	$190.95	$190.90
Purchase #6	$96.79	9.274%	$105.7663	$105.77	$105.75	$105.80
Purchase #7	$75.43	9.273%	$82.4246	$82.42	$82.40	$82.40
7 purchase totals =	$865.60		$940.2861	$940.28	$940.30	$940.20