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	$25.86	7.534%	$27.8083	$27.81	$27.80	$27.80
Purchase #2	$31.98	3.668%	$33.153	$33.15	$33.15	$33.20
Purchase #3	$97.94	3.474%	$101.3424	$101.34	$101.35	$101.30
Purchase #4	$96.86	6.822%	$103.4678	$103.47	$103.45	$103.50
Purchase #5	$149.52	11.158%	$166.2034	$166.20	$166.20	$166.20
Purchase #6	$118.26	7.391%	$127.0006	$127.00	$127.00	$127.00
Purchase #7	$86.89	5.629%	$91.781	$91.78	$91.80	$91.80
7 purchase totals =	$607.31		$650.7565	$650.75	$650.75	$650.80