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	$38.50	11.338%	$42.8651	$42.87	$42.85	$42.90
Purchase #2	$52.36	7.277%	$56.1702	$56.17	$56.15	$56.20
Purchase #3	$241.82	7.159%	$259.1319	$259.13	$259.15	$259.10
Purchase #4	$62.55	7.238%	$67.0774	$67.08	$67.10	$67.10
Purchase #5	$45.56	10.383%	$50.2905	$50.29	$50.30	$50.30
Purchase #6	$187.71	3.293%	$193.8913	$193.89	$193.90	$193.90
Purchase #7	$33.78	7.573%	$36.3382	$36.34	$36.35	$36.30
7 purchase totals =	$662.28		$705.7646	$705.77	$705.80	$705.80