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	$91.71	9.637%	$100.5481	$100.55	$100.55	$100.50
Purchase #2	$85.40	7.244%	$91.5864	$91.59	$91.60	$91.60
Purchase #3	$79.34	4.284%	$82.7389	$82.74	$82.75	$82.70
Purchase #4	$170.37	5.130%	$179.11	$179.11	$179.10	$179.10
Purchase #5	$175.65	3.233%	$181.3288	$181.33	$181.35	$181.30
Purchase #6	$122.59	8.535%	$133.0531	$133.05	$133.05	$133.10
Purchase #7	$20.41	6.842%	$21.8065	$21.81	$21.80	$21.80
7 purchase totals =	$745.47		$790.1718	$790.18	$790.20	$790.10