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	$5.90	9.484%	$6.4596	$6.46	$6.45	$6.50
Purchase #2	$180.91	5.812%	$191.4245	$191.42	$191.40	$191.40
Purchase #3	$65.69	4.123%	$68.3984	$68.40	$68.40	$68.40
Purchase #4	$37.81	10.537%	$41.794	$41.79	$41.80	$41.80
Purchase #5	$183.77	8.372%	$199.1552	$199.16	$199.15	$199.20
Purchase #6	$245.43	10.543%	$271.3057	$271.31	$271.30	$271.30
Purchase #7	$37.80	11.450%	$42.1281	$42.13	$42.15	$42.10
7 purchase totals =	$757.31		$820.6655	$820.67	$820.65	$820.70