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	$37.31	3.497%	$38.6147	$38.61	$38.60	$38.60
Purchase #2	$181.76	13.679%	$206.623	$206.62	$206.60	$206.60
Purchase #3	$47.90	13.189%	$54.2175	$54.22	$54.20	$54.20
Purchase #4	$76.43	9.537%	$83.7191	$83.72	$83.70	$83.70
Purchase #5	$242.84	11.702%	$271.2571	$271.26	$271.25	$271.30
Purchase #6	$182.56	3.435%	$188.8309	$188.83	$188.85	$188.80
Purchase #7	$39.67	8.664%	$43.107	$43.11	$43.10	$43.10
7 purchase totals =	$808.47		$886.3693	$886.37	$886.30	$886.30