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	$101.41	7.362%	$108.8758	$108.88	$108.90	$108.90
Purchase #2	$39.89	6.340%	$42.419	$42.42	$42.40	$42.40
Purchase #3	$129.65	11.568%	$144.6479	$144.65	$144.65	$144.60
Purchase #4	$94.65	5.870%	$100.206	$100.21	$100.20	$100.20
Purchase #5	$169.78	6.337%	$180.539	$180.54	$180.55	$180.50
Purchase #6	$183.25	3.465%	$189.5996	$189.60	$189.60	$189.60
Purchase #7	$188.68	8.420%	$204.5669	$204.57	$204.55	$204.60
7 purchase totals =	$907.31		$970.8542	$970.87	$970.85	$970.80