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	$20.35	4.554%	$21.2767	$21.28	$21.30	$21.30
Purchase #2	$114.35	6.699%	$122.0103	$122.01	$122.00	$122.00
Purchase #3	$61.54	10.356%	$67.9131	$67.91	$67.90	$67.90
Purchase #4	$108.96	3.521%	$112.7965	$112.80	$112.80	$112.80
Purchase #5	$30.65	13.834%	$34.8901	$34.89	$34.90	$34.90
Purchase #6	$41.75	11.341%	$46.4849	$46.48	$46.50	$46.50
Purchase #7	$41.62	9.113%	$45.4128	$45.41	$45.40	$45.40
7 purchase totals =	$419.22		$450.7844	$450.78	$450.80	$450.80