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	$29.82	4.848%	$31.2657	$31.27	$31.25	$31.30
Purchase #2	$249.89	5.569%	$263.8064	$263.81	$263.80	$263.80
Purchase #3	$91.32	7.325%	$98.0092	$98.01	$98.00	$98.00
Purchase #4	$235.64	5.351%	$248.2491	$248.25	$248.25	$248.20
Purchase #5	$64.56	11.545%	$72.0135	$72.01	$72.00	$72.00
Purchase #6	$167.39	3.336%	$172.9741	$172.97	$172.95	$173.00
Purchase #7	$101.65	9.292%	$111.0953	$111.10	$111.10	$111.10
7 purchase totals =	$940.27		$997.4133	$997.42	$997.35	$997.40