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	$53.68	3.856%	$55.7499	$55.75	$55.75	$55.70
Purchase #2	$203.74	3.127%	$210.1109	$210.11	$210.10	$210.10
Purchase #3	$83.50	7.764%	$89.9829	$89.98	$90.00	$90.00
Purchase #4	$217.60	9.770%	$238.8595	$238.86	$238.85	$238.90
Purchase #5	$211.34	10.416%	$233.3532	$233.35	$233.35	$233.40
Purchase #6	$133.94	4.214%	$139.5842	$139.58	$139.60	$139.60
Purchase #7	$113.70	5.222%	$119.6374	$119.64	$119.65	$119.60
7 purchase totals =	$1,017.50		$1,087.2780	$1,087.27	$1,087.30	$1,087.30