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	$80.52	12.180%	$90.3273	$90.33	$90.35	$90.30
Purchase #2	$221.57	12.621%	$249.5343	$249.53	$249.55	$249.50
Purchase #3	$43.52	5.269%	$45.8131	$45.81	$45.80	$45.80
Purchase #4	$67.77	4.610%	$70.8942	$70.89	$70.90	$70.90
Purchase #5	$249.82	4.761%	$261.7139	$261.71	$261.70	$261.70
Purchase #6	$115.42	8.799%	$125.5758	$125.58	$125.60	$125.60
Purchase #7	$183.70	5.275%	$193.3902	$193.39	$193.40	$193.40
7 purchase totals =	$962.32		$1,037.2488	$1,037.24	$1,037.30	$1,037.20