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	$248.73	13.756%	$282.9453	$282.95	$282.95	$282.90
Purchase #2	$81.87	9.542%	$89.682	$89.68	$89.70	$89.70
Purchase #3	$207.45	3.839%	$215.414	$215.41	$215.40	$215.40
Purchase #4	$165.74	13.790%	$188.5955	$188.60	$188.60	$188.60
Purchase #5	$16.70	10.759%	$18.4968	$18.50	$18.50	$18.50
Purchase #6	$41.98	10.669%	$46.4588	$46.46	$46.45	$46.50
Purchase #7	$237.89	9.165%	$259.6926	$259.69	$259.70	$259.70
7 purchase totals =	$1,000.36		$1,101.2850	$1,101.29	$1,101.30	$1,101.30