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	$43.79	4.784%	$45.8849	$45.88	$45.90	$45.90
Purchase #2	$215.48	8.705%	$234.2375	$234.24	$234.25	$234.20
Purchase #3	$130.60	4.385%	$136.3268	$136.33	$136.35	$136.30
Purchase #4	$139.57	7.123%	$149.5116	$149.51	$149.50	$149.50
Purchase #5	$148.83	7.128%	$159.4386	$159.44	$159.45	$159.40
Purchase #6	$131.45	12.440%	$147.8024	$147.80	$147.80	$147.80
Purchase #7	$94.49	11.724%	$105.568	$105.57	$105.55	$105.60
7 purchase totals =	$904.21		$978.7698	$978.77	$978.80	$978.70