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	$248.76	12.477%	$279.7978	$279.80	$279.80	$279.80
Purchase #2	$231.65	10.214%	$255.3107	$255.31	$255.30	$255.30
Purchase #3	$103.39	6.586%	$110.1993	$110.20	$110.20	$110.20
Purchase #4	$219.57	11.779%	$245.4332	$245.43	$245.45	$245.40
Purchase #5	$56.90	6.365%	$60.5217	$60.52	$60.50	$60.50
Purchase #6	$94.54	10.158%	$104.1434	$104.14	$104.15	$104.10
Purchase #7	$49.31	8.778%	$53.6384	$53.64	$53.65	$53.60
7 purchase totals =	$1,004.12		$1,109.0445	$1,109.04	$1,109.05	$1,108.90