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	$212.48	12.232%	$238.4706	$238.47	$238.45	$238.50
Purchase #2	$123.38	3.660%	$127.8957	$127.90	$127.90	$127.90
Purchase #3	$101.51	13.710%	$115.427	$115.43	$115.45	$115.40
Purchase #4	$227.43	10.600%	$251.5376	$251.54	$251.55	$251.50
Purchase #5	$55.37	4.744%	$57.9968	$58.00	$58.00	$58.00
Purchase #6	$140.41	10.861%	$155.6599	$155.66	$155.65	$155.70
Purchase #7	$50.92	10.716%	$56.3766	$56.38	$56.40	$56.40
7 purchase totals =	$911.50		$1,003.3642	$1,003.38	$1,003.40	$1,003.40