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	$238.62	7.206%	$255.815	$255.82	$255.80	$255.80
Purchase #2	$127.34	12.159%	$142.8233	$142.82	$142.80	$142.80
Purchase #3	$210.29	7.710%	$226.5034	$226.50	$226.50	$226.50
Purchase #4	$32.48	4.543%	$33.9556	$33.96	$33.95	$34.00
Purchase #5	$114.33	5.707%	$120.8548	$120.85	$120.85	$120.90
Purchase #6	$53.38	9.423%	$58.41	$58.41	$58.40	$58.40
Purchase #7	$160.51	12.485%	$180.5497	$180.55	$180.55	$180.50
7 purchase totals =	$936.95		$1,018.9118	$1,018.91	$1,018.85	$1,018.90