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	$244.50	12.573%	$275.241	$275.24	$275.25	$275.20
Purchase #2	$157.96	5.161%	$166.1123	$166.11	$166.10	$166.10
Purchase #3	$149.48	4.402%	$156.0601	$156.06	$156.05	$156.10
Purchase #4	$82.34	4.262%	$85.8493	$85.85	$85.85	$85.80
Purchase #5	$31.33	3.464%	$32.4153	$32.42	$32.40	$32.40
Purchase #6	$17.29	13.549%	$19.6326	$19.63	$19.65	$19.60
Purchase #7	$110.82	7.673%	$119.3232	$119.32	$119.30	$119.30
7 purchase totals =	$793.72		$854.6338	$854.63	$854.60	$854.50