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	$104.62	6.840%	$111.776	$111.78	$111.80	$111.80
Purchase #2	$213.53	8.440%	$231.5519	$231.55	$231.55	$231.60
Purchase #3	$109.84	4.616%	$114.9102	$114.91	$114.90	$114.90
Purchase #4	$77.98	10.320%	$86.0275	$86.03	$86.05	$86.00
Purchase #5	$86.41	9.281%	$94.4297	$94.43	$94.45	$94.40
Purchase #6	$36.66	10.739%	$40.5969	$40.60	$40.60	$40.60
Purchase #7	$21.30	13.176%	$24.1065	$24.11	$24.10	$24.10
7 purchase totals =	$650.34		$703.3987	$703.41	$703.45	$703.40