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	$76.64	7.663%	$82.5129	$82.51	$82.50	$82.50
Purchase #2	$236.92	13.788%	$269.5865	$269.59	$269.60	$269.60
Purchase #3	$138.33	7.270%	$148.3866	$148.39	$148.40	$148.40
Purchase #4	$23.57	10.761%	$26.1064	$26.11	$26.10	$26.10
Purchase #5	$117.76	10.731%	$130.3968	$130.40	$130.40	$130.40
Purchase #6	$230.29	5.300%	$242.4954	$242.50	$242.50	$242.50
Purchase #7	$225.88	11.499%	$251.8539	$251.85	$251.85	$251.90
7 purchase totals =	$1,049.39		$1,151.3385	$1,151.35	$1,151.35	$1,151.40