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	$16.60	11.343%	$18.4829	$18.48	$18.50	$18.50
Purchase #2	$119.43	3.127%	$123.1646	$123.16	$123.15	$123.20
Purchase #3	$36.32	5.412%	$38.2856	$38.29	$38.30	$38.30
Purchase #4	$60.75	5.533%	$64.1113	$64.11	$64.10	$64.10
Purchase #5	$40.69	4.276%	$42.4299	$42.43	$42.45	$42.40
Purchase #6	$171.70	5.392%	$180.9581	$180.96	$180.95	$181.00
Purchase #7	$30.52	4.561%	$31.912	$31.91	$31.90	$31.90
7 purchase totals =	$476.01		$499.3444	$499.34	$499.35	$499.40