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	$27.88	11.380%	$31.0527	$31.05	$31.05	$31.10
Purchase #2	$128.60	10.350%	$141.9101	$141.91	$141.90	$141.90
Purchase #3	$144.99	5.234%	$152.5788	$152.58	$152.60	$152.60
Purchase #4	$216.88	6.108%	$230.127	$230.13	$230.15	$230.10
Purchase #5	$114.50	11.310%	$127.45	$127.45	$127.45	$127.50
Purchase #6	$27.99	12.627%	$31.5243	$31.52	$31.50	$31.50
Purchase #7	$82.40	13.642%	$93.641	$93.64	$93.65	$93.60
7 purchase totals =	$743.24		$808.2839	$808.28	$808.30	$808.30