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	$7.84	9.689%	$8.5996	$8.60	$8.60	$8.60
Purchase #2	$76.59	7.853%	$82.6046	$82.60	$82.60	$82.60
Purchase #3	$115.55	3.580%	$119.6867	$119.69	$119.70	$119.70
Purchase #4	$133.49	13.515%	$151.5312	$151.53	$151.55	$151.50
Purchase #5	$175.72	3.748%	$182.306	$182.31	$182.30	$182.30
Purchase #6	$131.41	9.134%	$143.413	$143.41	$143.40	$143.40
Purchase #7	$118.81	7.261%	$127.4368	$127.44	$127.45	$127.40
7 purchase totals =	$759.41		$815.5779	$815.58	$815.60	$815.50