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	$188.34	12.781%	$212.4117	$212.41	$212.40	$212.40
Purchase #2	$88.48	9.204%	$96.6237	$96.62	$96.60	$96.60
Purchase #3	$156.76	13.600%	$178.0794	$178.08	$178.10	$178.10
Purchase #4	$169.61	10.127%	$186.7864	$186.79	$186.80	$186.80
Purchase #5	$238.28	13.501%	$270.4502	$270.45	$270.45	$270.50
Purchase #6	$54.44	13.654%	$61.8732	$61.87	$61.85	$61.90
Purchase #7	$12.62	4.577%	$13.1976	$13.20	$13.20	$13.20
7 purchase totals =	$908.53		$1,019.4222	$1,019.42	$1,019.40	$1,019.50