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	$111.71	6.613%	$119.0974	$119.10	$119.10	$119.10
Purchase #2	$187.65	5.547%	$198.0589	$198.06	$198.05	$198.10
Purchase #3	$114.73	7.759%	$123.6319	$123.63	$123.65	$123.60
Purchase #4	$99.61	7.257%	$106.8387	$106.84	$106.85	$106.80
Purchase #5	$47.74	13.367%	$54.1214	$54.12	$54.10	$54.10
Purchase #6	$37.82	11.332%	$42.1058	$42.11	$42.10	$42.10
Purchase #7	$172.80	7.652%	$186.0227	$186.02	$186.00	$186.00
7 purchase totals =	$772.06		$829.8768	$829.88	$829.85	$829.80