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	$12.61	3.612%	$13.0655	$13.07	$13.05	$13.10
Purchase #2	$74.33	5.817%	$78.6538	$78.65	$78.65	$78.70
Purchase #3	$65.38	11.487%	$72.8902	$72.89	$72.90	$72.90
Purchase #4	$41.48	7.673%	$44.6628	$44.66	$44.65	$44.70
Purchase #5	$92.25	7.616%	$99.2758	$99.28	$99.30	$99.30
Purchase #6	$12.89	12.214%	$14.4644	$14.46	$14.45	$14.50
Purchase #7	$202.51	11.632%	$226.066	$226.07	$226.05	$226.10
7 purchase totals =	$501.45		$549.0785	$549.08	$549.05	$549.30