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	$94.51	5.429%	$99.6409	$99.64	$99.65	$99.60
Purchase #2	$94.59	6.209%	$100.4631	$100.46	$100.45	$100.50
Purchase #3	$80.72	11.514%	$90.0141	$90.01	$90.00	$90.00
Purchase #4	$109.94	6.282%	$116.8464	$116.85	$116.85	$116.80
Purchase #5	$117.73	13.254%	$133.3339	$133.33	$133.35	$133.30
Purchase #6	$147.96	6.817%	$158.0464	$158.05	$158.05	$158.00
Purchase #7	$124.71	11.323%	$138.8309	$138.83	$138.85	$138.80
7 purchase totals =	$770.16		$837.1757	$837.17	$837.20	$837.00