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	$53.99	8.636%	$58.6526	$58.65	$58.65	$58.70
Purchase #2	$113.64	3.686%	$117.8288	$117.83	$117.85	$117.80
Purchase #3	$80.57	11.362%	$89.7244	$89.72	$89.70	$89.70
Purchase #4	$167.84	10.494%	$185.4531	$185.45	$185.45	$185.50
Purchase #5	$55.35	7.196%	$59.333	$59.33	$59.35	$59.30
Purchase #6	$200.79	4.438%	$209.7011	$209.70	$209.70	$209.70
Purchase #7	$172.59	11.190%	$191.9028	$191.90	$191.90	$191.90
7 purchase totals =	$844.77		$912.5958	$912.58	$912.60	$912.60