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	$49.35	13.299%	$55.9131	$55.91	$55.90	$55.90
Purchase #2	$72.48	9.735%	$79.5359	$79.54	$79.55	$79.50
Purchase #3	$13.41	7.563%	$14.4242	$14.42	$14.40	$14.40
Purchase #4	$34.62	7.617%	$37.257	$37.26	$37.25	$37.30
Purchase #5	$181.56	3.576%	$188.0526	$188.05	$188.05	$188.10
Purchase #6	$83.29	7.236%	$89.3169	$89.32	$89.30	$89.30
Purchase #7	$40.81	9.120%	$44.5319	$44.53	$44.55	$44.50
7 purchase totals =	$475.52		$509.0316	$509.03	$509.00	$509.00