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	$52.84	4.783%	$55.3673	$55.37	$55.35	$55.40
Purchase #2	$16.52	3.185%	$17.0462	$17.05	$17.05	$17.00
Purchase #3	$67.64	9.202%	$73.8642	$73.86	$73.85	$73.90
Purchase #4	$164.86	11.251%	$183.4084	$183.41	$183.40	$183.40
Purchase #5	$86.33	3.694%	$89.519	$89.52	$89.50	$89.50
Purchase #6	$168.37	5.770%	$178.0849	$178.08	$178.10	$178.10
Purchase #7	$47.82	12.333%	$53.7176	$53.72	$53.70	$53.70
7 purchase totals =	$604.38		$651.0076	$651.01	$650.95	$651.00