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	$79.73	7.364%	$85.6013	$85.60	$85.60	$85.60
Purchase #2	$48.55	10.810%	$53.7983	$53.80	$53.80	$53.80
Purchase #3	$123.37	5.790%	$130.5131	$130.51	$130.50	$130.50
Purchase #4	$114.27	9.832%	$125.505	$125.51	$125.50	$125.50
Purchase #5	$112.86	3.628%	$116.9546	$116.95	$116.95	$117.00
Purchase #6	$30.73	4.576%	$32.1362	$32.14	$32.15	$32.10
Purchase #7	$94.45	10.682%	$104.5391	$104.54	$104.55	$104.50
7 purchase totals =	$603.96		$649.0476	$649.05	$649.05	$649.00