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	$39.26	7.278%	$42.1173	$42.12	$42.10	$42.10
Purchase #2	$244.73	5.808%	$258.9439	$258.94	$258.95	$258.90
Purchase #3	$194.45	7.252%	$208.5515	$208.55	$208.55	$208.60
Purchase #4	$19.29	7.770%	$20.7888	$20.79	$20.80	$20.80
Purchase #5	$45.60	12.694%	$51.3885	$51.39	$51.40	$51.40
Purchase #6	$232.38	11.652%	$259.4569	$259.46	$259.45	$259.50
Purchase #7	$89.88	11.300%	$100.0364	$100.04	$100.05	$100.00
7 purchase totals =	$865.59		$941.2833	$941.29	$941.30	$941.30