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	$203.30	5.842%	$215.1768	$215.18	$215.20	$215.20
Purchase #2	$214.33	12.778%	$241.7171	$241.72	$241.70	$241.70
Purchase #3	$90.34	10.461%	$99.7905	$99.79	$99.80	$99.80
Purchase #4	$249.85	7.782%	$269.2933	$269.29	$269.30	$269.30
Purchase #5	$221.74	8.779%	$241.2066	$241.21	$241.20	$241.20
Purchase #6	$38.73	11.550%	$43.2033	$43.20	$43.20	$43.20
Purchase #7	$236.83	13.843%	$269.6144	$269.61	$269.60	$269.60
7 purchase totals =	$1,255.12		$1,380.0020	$1,380.00	$1,380.00	$1,380.00