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	$47.65	13.770%	$54.2114	$54.21	$54.20	$54.20
Purchase #2	$157.31	5.773%	$166.3915	$166.39	$166.40	$166.40
Purchase #3	$71.87	12.828%	$81.0895	$81.09	$81.10	$81.10
Purchase #4	$197.56	10.465%	$218.2347	$218.23	$218.25	$218.20
Purchase #5	$55.46	6.452%	$59.0383	$59.04	$59.05	$59.00
Purchase #6	$105.38	13.148%	$119.2354	$119.24	$119.25	$119.20
Purchase #7	$37.50	3.714%	$38.8928	$38.89	$38.90	$38.90
7 purchase totals =	$672.73		$737.0936	$737.09	$737.15	$737.00