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	$114.93	7.349%	$123.3762	$123.38	$123.40	$123.40
Purchase #2	$184.47	9.109%	$201.2734	$201.27	$201.25	$201.30
Purchase #3	$69.64	3.442%	$72.037	$72.04	$72.05	$72.00
Purchase #4	$67.73	6.210%	$71.936	$71.94	$71.95	$71.90
Purchase #5	$200.37	13.467%	$227.3538	$227.35	$227.35	$227.40
Purchase #6	$105.51	9.158%	$115.1726	$115.17	$115.15	$115.20
Purchase #7	$21.96	5.301%	$23.1241	$23.12	$23.10	$23.10
7 purchase totals =	$764.61		$834.2731	$834.27	$834.25	$834.30