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	$203.76	9.224%	$222.5548	$222.55	$222.55	$222.60
Purchase #2	$84.25	6.280%	$89.5409	$89.54	$89.55	$89.50
Purchase #3	$66.45	5.419%	$70.0509	$70.05	$70.05	$70.10
Purchase #4	$34.55	12.450%	$38.8515	$38.85	$38.85	$38.90
Purchase #5	$174.76	11.420%	$194.7176	$194.72	$194.70	$194.70
Purchase #6	$119.36	9.588%	$130.8042	$130.80	$130.80	$130.80
Purchase #7	$128.36	12.284%	$144.1277	$144.13	$144.15	$144.10
7 purchase totals =	$811.49		$890.6476	$890.64	$890.65	$890.70