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	$72.59	7.693%	$78.1743	$78.17	$78.15	$78.20
Purchase #2	$229.45	6.157%	$243.5772	$243.58	$243.60	$243.60
Purchase #3	$53.25	4.389%	$55.5871	$55.59	$55.60	$55.60
Purchase #4	$223.43	3.483%	$231.2121	$231.21	$231.20	$231.20
Purchase #5	$184.99	12.577%	$208.2562	$208.26	$208.25	$208.30
Purchase #6	$138.82	4.623%	$145.2376	$145.24	$145.25	$145.20
Purchase #7	$179.57	4.752%	$188.1032	$188.10	$188.10	$188.10
7 purchase totals =	$1,082.10		$1,150.1477	$1,150.15	$1,150.15	$1,150.20