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	$245.70	13.668%	$279.2823	$279.28	$279.30	$279.30
Purchase #2	$118.53	5.327%	$124.8441	$124.84	$124.85	$124.80
Purchase #3	$134.85	13.124%	$152.5477	$152.55	$152.55	$152.50
Purchase #4	$87.95	4.371%	$91.7943	$91.79	$91.80	$91.80
Purchase #5	$20.31	6.357%	$21.6011	$21.60	$21.60	$21.60
Purchase #6	$63.89	8.620%	$69.3973	$69.40	$69.40	$69.40
Purchase #7	$245.33	11.486%	$273.5086	$273.51	$273.50	$273.50
7 purchase totals =	$916.56		$1,012.9754	$1,012.97	$1,013.00	$1,012.90