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	$88.78	11.864%	$99.3129	$99.31	$99.30	$99.30
Purchase #2	$34.81	11.297%	$38.7425	$38.74	$38.75	$38.70
Purchase #3	$181.55	9.763%	$199.2747	$199.27	$199.25	$199.30
Purchase #4	$45.30	4.357%	$47.2737	$47.27	$47.25	$47.30
Purchase #5	$250.89	6.434%	$267.0323	$267.03	$267.05	$267.00
Purchase #6	$182.95	12.513%	$205.8425	$205.84	$205.85	$205.80
Purchase #7	$144.42	9.850%	$158.6454	$158.65	$158.65	$158.60
7 purchase totals =	$928.70		$1,016.1240	$1,016.11	$1,016.10	$1,016.00