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	$19.52	6.854%	$20.8579	$20.86	$20.85	$20.90
Purchase #2	$69.25	13.156%	$78.3605	$78.36	$78.35	$78.40
Purchase #3	$115.44	12.503%	$129.8735	$129.87	$129.85	$129.90
Purchase #4	$218.28	13.792%	$248.3852	$248.39	$248.40	$248.40
Purchase #5	$41.33	11.615%	$46.1305	$46.13	$46.15	$46.10
Purchase #6	$55.51	11.479%	$61.882	$61.88	$61.90	$61.90
Purchase #7	$89.92	10.575%	$99.429	$99.43	$99.45	$99.40
7 purchase totals =	$609.25		$684.9186	$684.92	$684.95	$685.00