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	$41.30	9.473%	$45.2123	$45.21	$45.20	$45.20
Purchase #2	$45.56	6.283%	$48.4225	$48.42	$48.40	$48.40
Purchase #3	$78.33	7.170%	$83.9463	$83.95	$83.95	$83.90
Purchase #4	$74.37	10.555%	$82.2198	$82.22	$82.20	$82.20
Purchase #5	$114.78	3.838%	$119.1853	$119.19	$119.20	$119.20
Purchase #6	$95.52	9.674%	$104.7606	$104.76	$104.75	$104.80
Purchase #7	$31.60	3.276%	$32.6352	$32.64	$32.65	$32.60
7 purchase totals =	$481.46		$516.3820	$516.39	$516.35	$516.30