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	$48.61	5.236%	$51.1552	$51.16	$51.15	$51.20
Purchase #2	$29.91	9.624%	$32.7885	$32.79	$32.80	$32.80
Purchase #3	$178.83	11.627%	$199.6226	$199.62	$199.60	$199.60
Purchase #4	$180.79	6.135%	$191.8815	$191.88	$191.90	$191.90
Purchase #5	$234.45	8.137%	$253.5272	$253.53	$253.55	$253.50
Purchase #6	$87.67	3.713%	$90.9252	$90.93	$90.95	$90.90
Purchase #7	$166.75	4.417%	$174.1153	$174.12	$174.10	$174.10
7 purchase totals =	$927.01		$994.0155	$994.03	$994.05	$994.00