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	$128.82	10.695%	$142.5973	$142.60	$142.60	$142.60
Purchase #2	$197.94	11.855%	$221.4058	$221.41	$221.40	$221.40
Purchase #3	$113.88	8.133%	$123.1419	$123.14	$123.15	$123.10
Purchase #4	$29.80	12.390%	$33.4922	$33.49	$33.50	$33.50
Purchase #5	$107.86	11.258%	$120.0029	$120.00	$120.00	$120.00
Purchase #6	$18.62	13.428%	$21.1203	$21.12	$21.10	$21.10
Purchase #7	$68.65	11.405%	$76.4795	$76.48	$76.50	$76.50
7 purchase totals =	$665.57		$738.2399	$738.24	$738.25	$738.20