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	$231.47	6.326%	$246.1128	$246.11	$246.10	$246.10
Purchase #2	$103.89	7.631%	$111.8178	$111.82	$111.80	$111.80
Purchase #3	$171.70	11.350%	$191.188	$191.19	$191.20	$191.20
Purchase #4	$59.56	8.552%	$64.6536	$64.65	$64.65	$64.70
Purchase #5	$241.56	12.665%	$272.1536	$272.15	$272.15	$272.20
Purchase #6	$25.45	7.497%	$27.358	$27.36	$27.35	$27.40
Purchase #7	$137.98	13.691%	$156.8708	$156.87	$156.85	$156.90
7 purchase totals =	$971.61		$1,070.1546	$1,070.15	$1,070.10	$1,070.30