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	$90.94	13.804%	$103.4934	$103.49	$103.50	$103.50
Purchase #2	$27.89	13.184%	$31.567	$31.57	$31.55	$31.60
Purchase #3	$92.82	8.194%	$100.4257	$100.43	$100.45	$100.40
Purchase #4	$154.38	12.507%	$173.6883	$173.69	$173.70	$173.70
Purchase #5	$188.85	5.775%	$199.7561	$199.76	$199.75	$199.80
Purchase #6	$106.88	10.674%	$118.2884	$118.29	$118.30	$118.30
Purchase #7	$177.57	12.153%	$199.1501	$199.15	$199.15	$199.20
7 purchase totals =	$839.33		$926.3690	$926.38	$926.40	$926.50