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	$237.35	13.500%	$269.3923	$269.39	$269.40	$269.40
Purchase #2	$35.48	4.655%	$37.1316	$37.13	$37.15	$37.10
Purchase #3	$73.78	3.522%	$76.3785	$76.38	$76.40	$76.40
Purchase #4	$43.57	6.258%	$46.2966	$46.30	$46.30	$46.30
Purchase #5	$141.70	4.798%	$148.4988	$148.50	$148.50	$148.50
Purchase #6	$129.63	5.733%	$137.0617	$137.06	$137.05	$137.10
Purchase #7	$156.38	8.786%	$170.1195	$170.12	$170.10	$170.10
7 purchase totals =	$817.89		$884.8790	$884.88	$884.90	$884.90