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	$55.41	10.713%	$61.3461	$61.35	$61.35	$61.30
Purchase #2	$94.89	10.317%	$104.6798	$104.68	$104.70	$104.70
Purchase #3	$115.44	6.714%	$123.1906	$123.19	$123.20	$123.20
Purchase #4	$126.89	12.806%	$143.1395	$143.14	$143.15	$143.10
Purchase #5	$58.92	9.675%	$64.6205	$64.62	$64.60	$64.60
Purchase #6	$79.43	12.138%	$89.0712	$89.07	$89.05	$89.10
Purchase #7	$78.25	4.764%	$81.9778	$81.98	$82.00	$82.00
7 purchase totals =	$609.23		$668.0255	$668.03	$668.05	$668.00