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	$59.48	11.277%	$66.1876	$66.19	$66.20	$66.20
Purchase #2	$57.82	12.628%	$65.1215	$65.12	$65.10	$65.10
Purchase #3	$213.43	11.406%	$237.7738	$237.77	$237.75	$237.80
Purchase #4	$84.92	5.206%	$89.3409	$89.34	$89.35	$89.30
Purchase #5	$30.30	12.288%	$34.0233	$34.02	$34.00	$34.00
Purchase #6	$35.83	5.675%	$37.8634	$37.86	$37.85	$37.90
Purchase #7	$50.26	12.187%	$56.3852	$56.39	$56.40	$56.40
7 purchase totals =	$532.04		$586.6957	$586.69	$586.65	$586.70