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	$35.40	6.594%	$37.7343	$37.73	$37.75	$37.70
Purchase #2	$225.91	13.146%	$255.6081	$255.61	$255.60	$255.60
Purchase #3	$171.62	6.107%	$182.1008	$182.10	$182.10	$182.10
Purchase #4	$242.29	6.171%	$257.2417	$257.24	$257.25	$257.20
Purchase #5	$40.30	12.204%	$45.2182	$45.22	$45.20	$45.20
Purchase #6	$38.74	8.656%	$42.0933	$42.09	$42.10	$42.10
Purchase #7	$45.79	13.503%	$51.973	$51.97	$51.95	$52.00
7 purchase totals =	$800.05		$871.9694	$871.96	$871.95	$871.90