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	$218.82	9.364%	$239.3103	$239.31	$239.30	$239.30
Purchase #2	$150.89	10.739%	$167.0941	$167.09	$167.10	$167.10
Purchase #3	$84.97	13.698%	$96.6092	$96.61	$96.60	$96.60
Purchase #4	$206.47	12.153%	$231.5623	$231.56	$231.55	$231.60
Purchase #5	$39.54	4.791%	$41.4344	$41.43	$41.45	$41.40
Purchase #6	$140.62	4.572%	$147.0491	$147.05	$147.05	$147.00
Purchase #7	$74.51	7.195%	$79.871	$79.87	$79.85	$79.90
7 purchase totals =	$915.82		$1,002.9304	$1,002.92	$1,002.90	$1,002.90