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	$40.72	3.337%	$42.0788	$42.08	$42.10	$42.10
Purchase #2	$145.82	12.552%	$164.1233	$164.12	$164.10	$164.10
Purchase #3	$91.45	9.757%	$100.3728	$100.37	$100.35	$100.40
Purchase #4	$236.75	5.706%	$250.259	$250.26	$250.25	$250.30
Purchase #5	$114.64	3.155%	$118.2569	$118.26	$118.25	$118.30
Purchase #6	$248.25	3.449%	$256.8121	$256.81	$256.80	$256.80
Purchase #7	$132.97	4.800%	$139.3526	$139.35	$139.35	$139.40
7 purchase totals =	$1,010.60		$1,071.2555	$1,071.25	$1,071.20	$1,071.40