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	$115.83	13.627%	$131.6142	$131.61	$131.60	$131.60
Purchase #2	$187.36	6.288%	$199.1412	$199.14	$199.15	$199.10
Purchase #3	$78.69	13.429%	$89.2573	$89.26	$89.25	$89.30
Purchase #4	$224.48	13.280%	$254.2909	$254.29	$254.30	$254.30
Purchase #5	$126.33	10.209%	$139.227	$139.23	$139.25	$139.20
Purchase #6	$29.29	11.760%	$32.7345	$32.73	$32.75	$32.70
Purchase #7	$171.76	7.309%	$184.3139	$184.31	$184.30	$184.30
7 purchase totals =	$933.74		$1,030.5790	$1,030.57	$1,030.60	$1,030.50