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	$165.54	11.590%	$184.7261	$184.73	$184.75	$184.70
Purchase #2	$184.66	7.697%	$198.8733	$198.87	$198.85	$198.90
Purchase #3	$39.37	12.796%	$44.4078	$44.41	$44.40	$44.40
Purchase #4	$40.82	10.758%	$45.2114	$45.21	$45.20	$45.20
Purchase #5	$53.42	5.745%	$56.489	$56.49	$56.50	$56.50
Purchase #6	$25.85	10.195%	$28.4854	$28.49	$28.50	$28.50
Purchase #7	$40.43	5.837%	$42.7899	$42.79	$42.80	$42.80
7 purchase totals =	$550.09		$600.9829	$600.99	$601.00	$601.00