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	$105.56	13.751%	$120.0756	$120.08	$120.10	$120.10
Purchase #2	$209.81	9.679%	$230.1175	$230.12	$230.10	$230.10
Purchase #3	$209.40	12.366%	$235.2944	$235.29	$235.30	$235.30
Purchase #4	$79.80	12.638%	$89.8851	$89.89	$89.90	$89.90
Purchase #5	$138.92	11.823%	$155.3445	$155.34	$155.35	$155.30
Purchase #6	$52.63	12.824%	$59.3793	$59.38	$59.40	$59.40
Purchase #7	$118.28	4.396%	$123.4796	$123.48	$123.50	$123.50
7 purchase totals =	$914.40		$1,013.5760	$1,013.58	$1,013.65	$1,013.60