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	$36.47	7.819%	$39.3216	$39.32	$39.30	$39.30
Purchase #2	$223.46	5.190%	$235.0576	$235.06	$235.05	$235.10
Purchase #3	$200.69	10.850%	$222.4649	$222.46	$222.45	$222.50
Purchase #4	$52.33	6.470%	$55.7158	$55.72	$55.70	$55.70
Purchase #5	$57.32	10.518%	$63.3489	$63.35	$63.35	$63.30
Purchase #6	$171.81	11.835%	$192.1437	$192.14	$192.15	$192.10
Purchase #7	$167.85	12.348%	$188.5761	$188.58	$188.60	$188.60
7 purchase totals =	$909.93		$996.6286	$996.63	$996.60	$996.60