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	$52.47	4.589%	$54.8778	$54.88	$54.90	$54.90
Purchase #2	$178.32	5.596%	$188.2988	$188.30	$188.30	$188.30
Purchase #3	$239.56	13.807%	$272.636	$272.64	$272.65	$272.60
Purchase #4	$100.99	10.799%	$111.8959	$111.90	$111.90	$111.90
Purchase #5	$38.31	9.805%	$42.0663	$42.07	$42.05	$42.10
Purchase #6	$169.80	8.469%	$184.1804	$184.18	$184.20	$184.20
Purchase #7	$62.98	7.179%	$67.5013	$67.50	$67.50	$67.50
7 purchase totals =	$842.43		$921.4565	$921.47	$921.50	$921.50