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	$85.40	6.195%	$90.6905	$90.69	$90.70	$90.70
Purchase #2	$162.32	6.531%	$172.9211	$172.92	$172.90	$172.90
Purchase #3	$229.87	4.636%	$240.5268	$240.53	$240.55	$240.50
Purchase #4	$85.73	13.740%	$97.5093	$97.51	$97.50	$97.50
Purchase #5	$164.74	11.758%	$184.1101	$184.11	$184.10	$184.10
Purchase #6	$38.71	10.582%	$42.8063	$42.81	$42.80	$42.80
Purchase #7	$61.40	7.274%	$65.8662	$65.87	$65.85	$65.90
7 purchase totals =	$828.17		$894.4303	$894.44	$894.40	$894.40