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	$227.37	12.482%	$255.7503	$255.75	$255.75	$255.80
Purchase #2	$245.87	7.641%	$264.6569	$264.66	$264.65	$264.70
Purchase #3	$240.32	6.599%	$256.1787	$256.18	$256.20	$256.20
Purchase #4	$92.98	6.357%	$98.8907	$98.89	$98.90	$98.90
Purchase #5	$26.85	4.351%	$28.0182	$28.02	$28.00	$28.00
Purchase #6	$7.50	4.342%	$7.8257	$7.83	$7.85	$7.80
Purchase #7	$122.56	13.477%	$139.0774	$139.08	$139.10	$139.10
7 purchase totals =	$963.45		$1,050.3979	$1,050.41	$1,050.45	$1,050.50