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	$5.80	11.381%	$6.4601	$6.46	$6.45	$6.50
Purchase #2	$231.90	9.784%	$254.5891	$254.59	$254.60	$254.60
Purchase #3	$212.31	8.820%	$231.0357	$231.04	$231.05	$231.00
Purchase #4	$215.31	12.543%	$242.3163	$242.32	$242.30	$242.30
Purchase #5	$61.37	5.785%	$64.9203	$64.92	$64.90	$64.90
Purchase #6	$172.32	3.570%	$178.4718	$178.47	$178.45	$178.50
Purchase #7	$137.97	9.721%	$151.3821	$151.38	$151.40	$151.40
7 purchase totals =	$1,036.98		$1,129.1754	$1,129.18	$1,129.15	$1,129.20