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	$70.35	7.807%	$75.8422	$75.84	$75.85	$75.80
Purchase #2	$141.77	13.217%	$160.5077	$160.51	$160.50	$160.50
Purchase #3	$49.28	7.842%	$53.1445	$53.14	$53.15	$53.10
Purchase #4	$153.94	9.113%	$167.9686	$167.97	$167.95	$168.00
Purchase #5	$90.25	6.264%	$95.9033	$95.90	$95.90	$95.90
Purchase #6	$137.88	9.561%	$151.0627	$151.06	$151.05	$151.10
Purchase #7	$92.66	12.115%	$103.8858	$103.89	$103.90	$103.90
7 purchase totals =	$736.13		$808.3148	$808.31	$808.30	$808.30