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	$116.59	12.583%	$131.2605	$131.26	$131.25	$131.30
Purchase #2	$234.44	12.206%	$263.0557	$263.06	$263.05	$263.10
Purchase #3	$189.68	4.694%	$198.5836	$198.58	$198.60	$198.60
Purchase #4	$197.88	13.511%	$224.6156	$224.62	$224.60	$224.60
Purchase #5	$6.81	3.650%	$7.0586	$7.06	$7.05	$7.10
Purchase #6	$174.93	9.344%	$191.2755	$191.28	$191.30	$191.30
Purchase #7	$18.39	13.784%	$20.9249	$20.92	$20.90	$20.90
7 purchase totals =	$938.72		$1,036.7744	$1,036.78	$1,036.75	$1,036.90