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	$246.81	7.186%	$264.5458	$264.55	$264.55	$264.50
Purchase #2	$109.73	8.716%	$119.2941	$119.29	$119.30	$119.30
Purchase #3	$72.33	13.592%	$82.1611	$82.16	$82.15	$82.20
Purchase #4	$157.45	12.590%	$177.273	$177.27	$177.25	$177.30
Purchase #5	$173.91	13.230%	$196.9183	$196.92	$196.90	$196.90
Purchase #6	$131.84	10.205%	$145.2943	$145.29	$145.30	$145.30
Purchase #7	$98.51	7.174%	$105.5771	$105.58	$105.60	$105.60
7 purchase totals =	$990.58		$1,091.0637	$1,091.06	$1,091.05	$1,091.10