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	$85.93	4.514%	$89.8089	$89.81	$89.80	$89.80
Purchase #2	$166.79	10.205%	$183.8109	$183.81	$183.80	$183.80
Purchase #3	$57.58	10.720%	$63.7526	$63.75	$63.75	$63.80
Purchase #4	$80.76	12.387%	$90.7637	$90.76	$90.75	$90.80
Purchase #5	$245.30	3.807%	$254.6386	$254.64	$254.65	$254.60
Purchase #6	$174.94	9.685%	$191.8829	$191.88	$191.90	$191.90
Purchase #7	$194.51	8.505%	$211.0531	$211.05	$211.05	$211.10
7 purchase totals =	$1,005.81		$1,085.7107	$1,085.70	$1,085.70	$1,085.80