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	$42.81	11.690%	$47.8145	$47.81	$47.80	$47.80
Purchase #2	$38.46	10.572%	$42.526	$42.53	$42.55	$42.50
Purchase #3	$17.98	3.181%	$18.5519	$18.55	$18.55	$18.60
Purchase #4	$111.66	5.736%	$118.0648	$118.06	$118.05	$118.10
Purchase #5	$188.36	13.873%	$214.4912	$214.49	$214.50	$214.50
Purchase #6	$180.38	6.323%	$191.7854	$191.79	$191.80	$191.80
Purchase #7	$67.32	8.297%	$72.9055	$72.91	$72.90	$72.90
7 purchase totals =	$646.97		$706.1393	$706.14	$706.15	$706.20