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	$86.76	7.810%	$93.536	$93.54	$93.55	$93.50
Purchase #2	$173.74	10.755%	$192.4257	$192.43	$192.45	$192.40
Purchase #3	$240.33	11.568%	$268.1314	$268.13	$268.15	$268.10
Purchase #4	$99.57	4.261%	$103.8127	$103.81	$103.80	$103.80
Purchase #5	$74.83	5.783%	$79.1574	$79.16	$79.15	$79.20
Purchase #6	$103.57	8.850%	$112.7359	$112.74	$112.75	$112.70
Purchase #7	$65.67	8.838%	$71.4739	$71.47	$71.45	$71.50
7 purchase totals =	$844.47		$921.2730	$921.28	$921.30	$921.20