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	$135.51	3.685%	$140.5035	$140.50	$140.50	$140.50
Purchase #2	$184.63	3.663%	$191.393	$191.39	$191.40	$191.40
Purchase #3	$57.76	10.558%	$63.8583	$63.86	$63.85	$63.90
Purchase #4	$18.65	3.756%	$19.3505	$19.35	$19.35	$19.40
Purchase #5	$71.42	9.807%	$78.4242	$78.42	$78.40	$78.40
Purchase #6	$239.66	6.581%	$255.432	$255.43	$255.45	$255.40
Purchase #7	$88.27	3.603%	$91.4504	$91.45	$91.45	$91.50
7 purchase totals =	$795.90		$840.4119	$840.40	$840.40	$840.50