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	$108.65	9.612%	$119.0934	$119.09	$119.10	$119.10
Purchase #2	$35.78	10.587%	$39.568	$39.57	$39.55	$39.60
Purchase #3	$247.64	8.457%	$268.5829	$268.58	$268.60	$268.60
Purchase #4	$214.83	9.144%	$234.4741	$234.47	$234.45	$234.50
Purchase #5	$55.60	6.705%	$59.328	$59.33	$59.35	$59.30
Purchase #6	$148.25	8.113%	$160.2775	$160.28	$160.30	$160.30
Purchase #7	$74.66	10.698%	$82.6471	$82.65	$82.65	$82.60
7 purchase totals =	$885.41		$963.9710	$963.97	$964.00	$964.00