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	$62.89	12.556%	$70.7865	$70.79	$70.80	$70.80
Purchase #2	$164.89	12.111%	$184.8598	$184.86	$184.85	$184.90
Purchase #3	$59.92	13.322%	$67.9025	$67.90	$67.90	$67.90
Purchase #4	$186.34	3.637%	$193.1172	$193.12	$193.10	$193.10
Purchase #5	$69.28	12.832%	$78.17	$78.17	$78.15	$78.20
Purchase #6	$53.43	11.307%	$59.4713	$59.47	$59.45	$59.50
Purchase #7	$145.47	3.116%	$150.0028	$150.00	$150.00	$150.00
7 purchase totals =	$742.22		$804.3101	$804.31	$804.25	$804.40