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	$80.79	3.347%	$83.494	$83.49	$83.50	$83.50
Purchase #2	$182.25	12.189%	$204.4645	$204.46	$204.45	$204.50
Purchase #3	$117.49	5.372%	$123.8016	$123.80	$123.80	$123.80
Purchase #4	$14.98	5.253%	$15.7669	$15.77	$15.75	$15.80
Purchase #5	$39.75	6.851%	$42.4733	$42.47	$42.45	$42.50
Purchase #6	$107.66	7.528%	$115.7646	$115.76	$115.75	$115.80
Purchase #7	$238.29	10.847%	$264.1373	$264.14	$264.15	$264.10
7 purchase totals =	$781.21		$849.9022	$849.89	$849.85	$850.00