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	$204.44	4.379%	$213.3924	$213.39	$213.40	$213.40
Purchase #2	$207.78	10.138%	$228.8447	$228.84	$228.85	$228.80
Purchase #3	$184.51	8.789%	$200.7266	$200.73	$200.75	$200.70
Purchase #4	$140.75	7.369%	$151.1219	$151.12	$151.10	$151.10
Purchase #5	$238.83	12.219%	$268.0126	$268.01	$268.00	$268.00
Purchase #6	$71.78	13.719%	$81.6275	$81.63	$81.65	$81.60
Purchase #7	$100.54	12.254%	$112.8602	$112.86	$112.85	$112.90
7 purchase totals =	$1,148.63		$1,256.5859	$1,256.58	$1,256.60	$1,256.50