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	$72.47	3.499%	$75.0057	$75.01	$75.00	$75.00
Purchase #2	$21.82	7.500%	$23.4565	$23.46	$23.45	$23.50
Purchase #3	$29.72	6.732%	$31.7208	$31.72	$31.70	$31.70
Purchase #4	$23.34	3.816%	$24.2307	$24.23	$24.25	$24.20
Purchase #5	$123.39	3.419%	$127.6087	$127.61	$127.60	$127.60
Purchase #6	$163.55	6.814%	$174.6943	$174.69	$174.70	$174.70
Purchase #7	$90.52	11.280%	$100.7307	$100.73	$100.75	$100.70
7 purchase totals =	$524.81		$557.4474	$557.45	$557.45	$557.40