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	$179.74	3.701%	$186.3922	$186.39	$186.40	$186.40
Purchase #2	$38.38	11.817%	$42.9154	$42.92	$42.90	$42.90
Purchase #3	$223.45	13.609%	$253.8593	$253.86	$253.85	$253.90
Purchase #4	$54.36	5.193%	$57.1829	$57.18	$57.20	$57.20
Purchase #5	$242.61	11.393%	$270.2506	$270.25	$270.25	$270.30
Purchase #6	$31.61	13.501%	$35.8777	$35.88	$35.90	$35.90
Purchase #7	$139.92	8.511%	$151.8286	$151.83	$151.85	$151.80
7 purchase totals =	$910.07		$998.3067	$998.31	$998.35	$998.40