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	$17.44	6.417%	$18.5591	$18.56	$18.55	$18.60
Purchase #2	$82.44	8.702%	$89.6139	$89.61	$89.60	$89.60
Purchase #3	$207.35	7.277%	$222.4389	$222.44	$222.45	$222.40
Purchase #4	$5.96	7.700%	$6.4189	$6.42	$6.40	$6.40
Purchase #5	$39.71	5.104%	$41.7368	$41.74	$41.75	$41.70
Purchase #6	$51.35	10.835%	$56.9138	$56.91	$56.90	$56.90
Purchase #7	$215.69	4.553%	$225.5104	$225.51	$225.50	$225.50
7 purchase totals =	$619.94		$661.1918	$661.19	$661.15	$661.10