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	$46.48	9.347%	$50.8245	$50.82	$50.80	$50.80
Purchase #2	$35.36	13.284%	$40.0572	$40.06	$40.05	$40.10
Purchase #3	$63.43	4.140%	$66.056	$66.06	$66.05	$66.10
Purchase #4	$233.77	5.564%	$246.777	$246.78	$246.80	$246.80
Purchase #5	$166.49	11.661%	$185.9044	$185.90	$185.90	$185.90
Purchase #6	$134.90	8.665%	$146.5891	$146.59	$146.60	$146.60
Purchase #7	$133.76	10.373%	$147.6349	$147.63	$147.65	$147.60
7 purchase totals =	$814.19		$883.8431	$883.84	$883.85	$883.90