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	$80.96	13.411%	$91.8175	$91.82	$91.80	$91.80
Purchase #2	$17.27	10.188%	$19.0295	$19.03	$19.05	$19.00
Purchase #3	$30.60	3.444%	$31.6539	$31.65	$31.65	$31.70
Purchase #4	$10.28	11.604%	$11.4729	$11.47	$11.45	$11.50
Purchase #5	$39.80	13.396%	$45.1316	$45.13	$45.15	$45.10
Purchase #6	$74.71	10.781%	$82.7645	$82.76	$82.75	$82.80
Purchase #7	$39.93	6.317%	$42.4524	$42.45	$42.45	$42.50
7 purchase totals =	$293.55		$324.3223	$324.31	$324.30	$324.40