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	$78.48	11.229%	$87.2925	$87.29	$87.30	$87.30
Purchase #2	$180.57	10.798%	$200.0679	$200.07	$200.05	$200.10
Purchase #3	$48.37	9.535%	$52.9821	$52.98	$53.00	$53.00
Purchase #4	$66.67	5.121%	$70.0842	$70.08	$70.10	$70.10
Purchase #5	$200.89	12.423%	$225.8466	$225.85	$225.85	$225.80
Purchase #6	$197.46	8.704%	$214.6469	$214.65	$214.65	$214.60
Purchase #7	$151.90	9.851%	$166.8637	$166.86	$166.85	$166.90
7 purchase totals =	$924.34		$1,017.7839	$1,017.78	$1,017.80	$1,017.80