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	$84.52	5.526%	$89.1906	$89.19	$89.20	$89.20
Purchase #2	$62.91	5.289%	$66.2373	$66.24	$66.25	$66.20
Purchase #3	$23.69	6.759%	$25.2912	$25.29	$25.30	$25.30
Purchase #4	$65.75	10.717%	$72.7964	$72.80	$72.80	$72.80
Purchase #5	$133.44	3.248%	$137.7741	$137.77	$137.75	$137.80
Purchase #6	$160.81	10.801%	$178.1791	$178.18	$178.20	$178.20
Purchase #7	$215.73	10.366%	$238.0926	$238.09	$238.10	$238.10
7 purchase totals =	$746.85		$807.5613	$807.56	$807.60	$807.60