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	$103.80	7.109%	$111.1791	$111.18	$111.20	$111.20
Purchase #2	$250.30	7.499%	$269.07	$269.07	$269.05	$269.10
Purchase #3	$25.83	9.693%	$28.3337	$28.33	$28.35	$28.30
Purchase #4	$59.59	5.295%	$62.7453	$62.75	$62.75	$62.70
Purchase #5	$200.28	11.271%	$222.8536	$222.85	$222.85	$222.90
Purchase #6	$139.78	4.347%	$145.8562	$145.86	$145.85	$145.90
Purchase #7	$76.83	8.774%	$83.5711	$83.57	$83.55	$83.60
7 purchase totals =	$856.41		$923.6090	$923.61	$923.60	$923.70