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	$29.97	11.787%	$33.5026	$33.50	$33.50	$33.50
Purchase #2	$161.84	6.575%	$172.481	$172.48	$172.50	$172.50
Purchase #3	$72.58	8.259%	$78.5744	$78.57	$78.55	$78.60
Purchase #4	$129.81	12.728%	$146.3322	$146.33	$146.35	$146.30
Purchase #5	$153.68	6.116%	$163.0791	$163.08	$163.10	$163.10
Purchase #6	$168.38	6.776%	$179.7894	$179.79	$179.80	$179.80
Purchase #7	$29.35	11.453%	$32.7115	$32.71	$32.70	$32.70
7 purchase totals =	$745.61		$806.4702	$806.46	$806.50	$806.50