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	$250.47	13.670%	$284.7092	$284.71	$284.70	$284.70
Purchase #2	$37.56	11.243%	$41.7829	$41.78	$41.80	$41.80
Purchase #3	$37.38	12.858%	$42.1863	$42.19	$42.20	$42.20
Purchase #4	$93.49	5.573%	$98.7002	$98.70	$98.70	$98.70
Purchase #5	$147.47	12.504%	$165.9096	$165.91	$165.90	$165.90
Purchase #6	$49.81	4.612%	$52.1072	$52.11	$52.10	$52.10
Purchase #7	$76.57	5.259%	$80.5968	$80.60	$80.60	$80.60
7 purchase totals =	$692.75		$765.9922	$766.00	$766.00	$766.00