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	$224.61	3.247%	$231.9031	$231.90	$231.90	$231.90
Purchase #2	$167.46	9.578%	$183.4993	$183.50	$183.50	$183.50
Purchase #3	$133.35	8.278%	$144.3887	$144.39	$144.40	$144.40
Purchase #4	$25.86	11.805%	$28.9128	$28.91	$28.90	$28.90
Purchase #5	$232.82	13.710%	$264.7396	$264.74	$264.75	$264.70
Purchase #6	$98.31	5.681%	$103.895	$103.90	$103.90	$103.90
Purchase #7	$45.73	10.142%	$50.3679	$50.37	$50.35	$50.40
7 purchase totals =	$928.14		$1,007.7064	$1,007.71	$1,007.70	$1,007.70