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	$68.89	13.410%	$78.1281	$78.13	$78.15	$78.10
Purchase #2	$178.50	8.850%	$194.2973	$194.30	$194.30	$194.30
Purchase #3	$96.28	8.196%	$104.1711	$104.17	$104.15	$104.20
Purchase #4	$197.55	5.846%	$209.0988	$209.10	$209.10	$209.10
Purchase #5	$163.71	5.680%	$173.0087	$173.01	$173.00	$173.00
Purchase #6	$229.27	8.483%	$248.719	$248.72	$248.70	$248.70
Purchase #7	$70.25	3.585%	$72.7685	$72.77	$72.75	$72.80
7 purchase totals =	$1,004.45		$1,080.1915	$1,080.20	$1,080.15	$1,080.20