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	$163.59	3.166%	$168.7693	$168.77	$168.75	$168.80
Purchase #2	$138.75	11.713%	$155.0018	$155.00	$155.00	$155.00
Purchase #3	$200.38	9.136%	$218.6867	$218.69	$218.70	$218.70
Purchase #4	$28.31	10.625%	$31.3179	$31.32	$31.30	$31.30
Purchase #5	$90.49	10.693%	$100.1661	$100.17	$100.15	$100.20
Purchase #6	$124.81	5.641%	$131.8505	$131.85	$131.85	$131.90
Purchase #7	$91.65	12.346%	$102.9651	$102.97	$102.95	$103.00
7 purchase totals =	$837.98		$908.7574	$908.77	$908.70	$908.90