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	$139.30	6.105%	$147.8043	$147.80	$147.80	$147.80
Purchase #2	$91.47	9.753%	$100.3911	$100.39	$100.40	$100.40
Purchase #3	$207.33	4.214%	$216.0669	$216.07	$216.05	$216.10
Purchase #4	$116.38	6.316%	$123.7306	$123.73	$123.75	$123.70
Purchase #5	$104.95	13.745%	$119.3754	$119.38	$119.40	$119.40
Purchase #6	$182.73	4.141%	$190.2968	$190.30	$190.30	$190.30
Purchase #7	$215.93	8.379%	$234.0228	$234.02	$234.00	$234.00
7 purchase totals =	$1,058.09		$1,131.6879	$1,131.69	$1,131.70	$1,131.70