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	$203.95	13.491%	$231.4649	$231.46	$231.45	$231.50
Purchase #2	$37.88	12.233%	$42.5139	$42.51	$42.50	$42.50
Purchase #3	$160.33	9.708%	$175.8948	$175.89	$175.90	$175.90
Purchase #4	$158.94	6.165%	$168.7387	$168.74	$168.75	$168.70
Purchase #5	$112.71	9.271%	$123.1593	$123.16	$123.15	$123.20
Purchase #6	$167.64	4.204%	$174.6876	$174.69	$174.70	$174.70
Purchase #7	$162.73	7.422%	$174.8078	$174.81	$174.80	$174.80
7 purchase totals =	$1,004.18		$1,091.2670	$1,091.26	$1,091.25	$1,091.30