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	$194.66	9.145%	$212.4617	$212.46	$212.45	$212.50
Purchase #2	$53.45	4.861%	$56.0482	$56.05	$56.05	$56.00
Purchase #3	$152.28	9.740%	$167.1121	$167.11	$167.10	$167.10
Purchase #4	$63.35	8.799%	$68.9242	$68.92	$68.90	$68.90
Purchase #5	$208.86	6.525%	$222.4881	$222.49	$222.50	$222.50
Purchase #6	$89.77	11.424%	$100.0253	$100.03	$100.05	$100.00
Purchase #7	$155.85	10.201%	$171.7483	$171.75	$171.75	$171.70
7 purchase totals =	$918.22		$998.8079	$998.81	$998.80	$998.70