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	$179.54	4.247%	$187.1651	$187.17	$187.15	$187.20
Purchase #2	$22.80	7.524%	$24.5155	$24.52	$24.50	$24.50
Purchase #3	$250.31	5.787%	$264.7954	$264.80	$264.80	$264.80
Purchase #4	$241.56	13.388%	$273.9001	$273.90	$273.90	$273.90
Purchase #5	$100.80	13.161%	$114.0663	$114.07	$114.05	$114.10
Purchase #6	$40.31	12.793%	$45.4669	$45.47	$45.45	$45.50
Purchase #7	$31.80	7.530%	$34.1945	$34.19	$34.20	$34.20
7 purchase totals =	$867.12		$944.1038	$944.12	$944.05	$944.20