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	$28.88	12.578%	$32.5125	$32.51	$32.50	$32.50
Purchase #2	$221.86	4.787%	$232.4804	$232.48	$232.50	$232.50
Purchase #3	$101.87	6.127%	$108.1116	$108.11	$108.10	$108.10
Purchase #4	$171.45	7.264%	$183.9041	$183.90	$183.90	$183.90
Purchase #5	$145.51	7.428%	$156.3185	$156.32	$156.30	$156.30
Purchase #6	$102.83	5.164%	$108.1401	$108.14	$108.15	$108.10
Purchase #7	$146.55	3.758%	$152.0573	$152.06	$152.05	$152.10
7 purchase totals =	$918.95		$973.5245	$973.52	$973.50	$973.50