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	$54.72	5.261%	$57.5988	$57.60	$57.60	$57.60
Purchase #2	$105.37	3.837%	$109.413	$109.41	$109.40	$109.40
Purchase #3	$80.49	11.270%	$89.5612	$89.56	$89.55	$89.60
Purchase #4	$110.67	7.570%	$119.0477	$119.05	$119.05	$119.00
Purchase #5	$208.79	8.231%	$225.9755	$225.98	$226.00	$226.00
Purchase #6	$140.41	7.715%	$151.2426	$151.24	$151.25	$151.20
Purchase #7	$155.38	7.337%	$166.7802	$166.78	$166.80	$166.80
7 purchase totals =	$855.83		$919.6190	$919.62	$919.65	$919.60