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	$171.59	7.820%	$185.0083	$185.01	$185.00	$185.00
Purchase #2	$211.80	8.677%	$230.1779	$230.18	$230.20	$230.20
Purchase #3	$211.44	10.212%	$233.0323	$233.03	$233.05	$233.00
Purchase #4	$98.79	5.547%	$104.2699	$104.27	$104.25	$104.30
Purchase #5	$244.72	4.829%	$256.5375	$256.54	$256.55	$256.50
Purchase #6	$73.88	7.303%	$79.2755	$79.28	$79.30	$79.30
Purchase #7	$85.83	5.539%	$90.5841	$90.58	$90.60	$90.60
7 purchase totals =	$1,098.05		$1,178.8855	$1,178.89	$1,178.95	$1,178.90