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	$234.83	3.597%	$243.2768	$243.28	$243.30	$243.30
Purchase #2	$168.83	12.490%	$189.9169	$189.92	$189.90	$189.90
Purchase #3	$61.28	7.644%	$65.9642	$65.96	$65.95	$66.00
Purchase #4	$96.86	3.238%	$99.9963	$100.00	$100.00	$100.00
Purchase #5	$17.52	6.252%	$18.6154	$18.62	$18.60	$18.60
Purchase #6	$52.40	6.127%	$55.6105	$55.61	$55.60	$55.60
Purchase #7	$182.78	11.567%	$203.9222	$203.92	$203.90	$203.90
7 purchase totals =	$814.50		$877.3023	$877.31	$877.25	$877.30