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	$148.31	13.417%	$168.2088	$168.21	$168.20	$168.20
Purchase #2	$212.52	6.254%	$225.811	$225.81	$225.80	$225.80
Purchase #3	$91.53	4.222%	$95.3944	$95.39	$95.40	$95.40
Purchase #4	$111.34	5.238%	$117.172	$117.17	$117.15	$117.20
Purchase #5	$76.39	7.789%	$82.34	$82.34	$82.35	$82.30
Purchase #6	$49.84	9.391%	$54.5205	$54.52	$54.50	$54.50
Purchase #7	$192.58	12.217%	$216.1075	$216.11	$216.10	$216.10
7 purchase totals =	$882.51		$959.5542	$959.55	$959.50	$959.50