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	$232.73	13.368%	$263.8413	$263.84	$263.85	$263.80
Purchase #2	$197.45	12.160%	$221.4599	$221.46	$221.45	$221.50
Purchase #3	$77.72	6.268%	$82.5915	$82.59	$82.60	$82.60
Purchase #4	$21.99	11.359%	$24.4878	$24.49	$24.50	$24.50
Purchase #5	$35.55	8.468%	$38.5604	$38.56	$38.55	$38.60
Purchase #6	$100.88	8.617%	$109.5728	$109.57	$109.55	$109.60
Purchase #7	$179.25	9.418%	$196.1318	$196.13	$196.15	$196.10
7 purchase totals =	$845.57		$936.6455	$936.64	$936.65	$936.70