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	$96.36	7.227%	$103.3239	$103.32	$103.30	$103.30
Purchase #2	$173.64	9.463%	$190.0716	$190.07	$190.05	$190.10
Purchase #3	$129.94	10.180%	$143.1679	$143.17	$143.15	$143.20
Purchase #4	$73.39	11.690%	$81.9693	$81.97	$81.95	$82.00
Purchase #5	$145.83	13.394%	$165.3625	$165.36	$165.35	$165.40
Purchase #6	$78.97	5.626%	$83.4129	$83.41	$83.40	$83.40
Purchase #7	$85.30	12.610%	$96.0563	$96.06	$96.05	$96.10
7 purchase totals =	$783.43		$863.3644	$863.36	$863.25	$863.50