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	$169.90	5.225%	$178.7773	$178.78	$178.80	$178.80
Purchase #2	$77.43	6.577%	$82.5226	$82.52	$82.50	$82.50
Purchase #3	$110.47	13.855%	$125.7756	$125.78	$125.80	$125.80
Purchase #4	$37.56	12.828%	$42.3782	$42.38	$42.40	$42.40
Purchase #5	$29.51	3.492%	$30.5405	$30.54	$30.55	$30.50
Purchase #6	$147.85	11.809%	$165.3096	$165.31	$165.30	$165.30
Purchase #7	$48.81	11.138%	$54.2465	$54.25	$54.25	$54.20
7 purchase totals =	$621.53		$679.5503	$679.56	$679.60	$679.50