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	$76.69	7.609%	$82.5253	$82.53	$82.55	$82.50
Purchase #2	$225.53	9.691%	$247.3861	$247.39	$247.40	$247.40
Purchase #3	$180.52	6.196%	$191.705	$191.71	$191.70	$191.70
Purchase #4	$183.77	11.247%	$204.4386	$204.44	$204.45	$204.40
Purchase #5	$54.97	10.720%	$60.8628	$60.86	$60.85	$60.90
Purchase #6	$80.71	11.305%	$89.8343	$89.83	$89.85	$89.80
Purchase #7	$50.39	6.764%	$53.7984	$53.80	$53.80	$53.80
7 purchase totals =	$852.58		$930.5505	$930.56	$930.60	$930.50