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	$20.41	5.273%	$21.4862	$21.49	$21.50	$21.50
Purchase #2	$167.76	13.810%	$190.9277	$190.93	$190.95	$190.90
Purchase #3	$231.35	5.701%	$244.5393	$244.54	$244.55	$244.50
Purchase #4	$41.64	4.681%	$43.5892	$43.59	$43.60	$43.60
Purchase #5	$56.83	12.242%	$63.7871	$63.79	$63.80	$63.80
Purchase #6	$142.25	8.490%	$154.327	$154.33	$154.35	$154.30
Purchase #7	$57.80	8.299%	$62.5968	$62.60	$62.60	$62.60
7 purchase totals =	$718.04		$781.2533	$781.27	$781.35	$781.20