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	$12.97	3.221%	$13.3878	$13.39	$13.40	$13.40
Purchase #2	$96.93	3.753%	$100.5678	$100.57	$100.55	$100.60
Purchase #3	$233.67	13.379%	$264.9327	$264.93	$264.95	$264.90
Purchase #4	$128.30	10.493%	$141.7625	$141.76	$141.75	$141.80
Purchase #5	$14.25	11.157%	$15.8399	$15.84	$15.85	$15.80
Purchase #6	$242.83	9.160%	$265.0732	$265.07	$265.05	$265.10
Purchase #7	$19.88	7.640%	$21.3988	$21.40	$21.40	$21.40
7 purchase totals =	$748.83		$822.9627	$822.96	$822.95	$823.00