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	$36.36	6.109%	$38.5812	$38.58	$38.60	$38.60
Purchase #2	$147.81	12.194%	$165.834	$165.83	$165.85	$165.80
Purchase #3	$72.38	6.697%	$77.2273	$77.23	$77.25	$77.20
Purchase #4	$74.98	3.515%	$77.6155	$77.62	$77.60	$77.60
Purchase #5	$48.88	12.660%	$55.0682	$55.07	$55.05	$55.10
Purchase #6	$45.48	3.828%	$47.221	$47.22	$47.20	$47.20
Purchase #7	$159.46	3.715%	$165.3839	$165.38	$165.40	$165.40
7 purchase totals =	$585.35		$626.9311	$626.93	$626.95	$626.90