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	$240.88	12.201%	$270.2698	$270.27	$270.25	$270.30
Purchase #2	$160.33	4.107%	$166.9148	$166.91	$166.90	$166.90
Purchase #3	$221.43	5.456%	$233.5112	$233.51	$233.50	$233.50
Purchase #4	$179.29	11.857%	$200.5484	$200.55	$200.55	$200.50
Purchase #5	$56.81	12.289%	$63.7914	$63.79	$63.80	$63.80
Purchase #6	$96.72	13.404%	$109.6843	$109.68	$109.70	$109.70
Purchase #7	$148.72	12.366%	$167.1107	$167.11	$167.10	$167.10
7 purchase totals =	$1,104.18		$1,211.8306	$1,211.82	$1,211.80	$1,211.80