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	$93.70	7.617%	$100.8371	$100.84	$100.85	$100.80
Purchase #2	$51.64	3.190%	$53.2873	$53.29	$53.30	$53.30
Purchase #3	$202.68	12.394%	$227.8002	$227.80	$227.80	$227.80
Purchase #4	$138.96	11.766%	$155.31	$155.31	$155.30	$155.30
Purchase #5	$245.40	11.133%	$272.7204	$272.72	$272.70	$272.70
Purchase #6	$78.57	6.245%	$83.4767	$83.48	$83.50	$83.50
Purchase #7	$84.68	5.206%	$89.0884	$89.09	$89.10	$89.10
7 purchase totals =	$895.63		$982.5201	$982.53	$982.55	$982.50