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	$30.89	9.708%	$33.8888	$33.89	$33.90	$33.90
Purchase #2	$123.48	10.311%	$136.212	$136.21	$136.20	$136.20
Purchase #3	$117.81	5.241%	$123.9844	$123.98	$124.00	$124.00
Purchase #4	$150.52	10.468%	$166.2764	$166.28	$166.30	$166.30
Purchase #5	$106.80	11.340%	$118.9111	$118.91	$118.90	$118.90
Purchase #6	$150.72	10.175%	$166.0558	$166.06	$166.05	$166.10
Purchase #7	$173.27	7.269%	$185.865	$185.87	$185.85	$185.90
7 purchase totals =	$853.49		$931.1935	$931.20	$931.20	$931.30