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	$64.66	12.580%	$72.7942	$72.79	$72.80	$72.80
Purchase #2	$184.30	11.530%	$205.5498	$205.55	$205.55	$205.50
Purchase #3	$212.42	11.193%	$236.1962	$236.20	$236.20	$236.20
Purchase #4	$135.43	10.645%	$149.8465	$149.85	$149.85	$149.80
Purchase #5	$162.94	3.656%	$168.8971	$168.90	$168.90	$168.90
Purchase #6	$123.56	3.585%	$127.9896	$127.99	$128.00	$128.00
Purchase #7	$39.64	6.346%	$42.1556	$42.16	$42.15	$42.20
7 purchase totals =	$922.95		$1,003.4290	$1,003.44	$1,003.45	$1,003.40