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	$169.93	11.727%	$189.8577	$189.86	$189.85	$189.90
Purchase #2	$89.95	4.848%	$94.3108	$94.31	$94.30	$94.30
Purchase #3	$193.82	7.781%	$208.9011	$208.90	$208.90	$208.90
Purchase #4	$96.88	4.314%	$101.0594	$101.06	$101.05	$101.10
Purchase #5	$81.29	9.612%	$89.1036	$89.10	$89.10	$89.10
Purchase #6	$85.85	13.594%	$97.5204	$97.52	$97.50	$97.50
Purchase #7	$146.91	4.373%	$153.3344	$153.33	$153.35	$153.30
7 purchase totals =	$864.63		$934.0874	$934.08	$934.05	$934.10