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	$19.49	7.410%	$20.9342	$20.93	$20.95	$20.90
Purchase #2	$200.31	8.685%	$217.7069	$217.71	$217.70	$217.70
Purchase #3	$52.42	7.608%	$56.4081	$56.41	$56.40	$56.40
Purchase #4	$171.36	11.758%	$191.5085	$191.51	$191.50	$191.50
Purchase #5	$52.97	9.678%	$58.0964	$58.10	$58.10	$58.10
Purchase #6	$162.66	3.209%	$167.8798	$167.88	$167.90	$167.90
Purchase #7	$127.40	3.468%	$131.8182	$131.82	$131.80	$131.80
7 purchase totals =	$786.61		$844.3521	$844.36	$844.35	$844.30