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	$89.84	11.539%	$100.2066	$100.21	$100.20	$100.20
Purchase #2	$182.94	5.694%	$193.3566	$193.36	$193.35	$193.40
Purchase #3	$109.32	11.220%	$121.5857	$121.59	$121.60	$121.60
Purchase #4	$107.75	9.831%	$118.3429	$118.34	$118.35	$118.30
Purchase #5	$107.75	3.289%	$111.2939	$111.29	$111.30	$111.30
Purchase #6	$220.66	10.360%	$243.5204	$243.52	$243.50	$243.50
Purchase #7	$130.46	10.237%	$143.8152	$143.82	$143.80	$143.80
7 purchase totals =	$948.72		$1,032.1213	$1,032.13	$1,032.10	$1,032.10