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	$115.95	13.302%	$131.3737	$131.37	$131.35	$131.40
Purchase #2	$150.50	5.590%	$158.913	$158.91	$158.90	$158.90
Purchase #3	$93.67	6.733%	$99.9768	$99.98	$100.00	$100.00
Purchase #4	$154.67	11.688%	$172.7478	$172.75	$172.75	$172.70
Purchase #5	$143.89	12.715%	$162.1856	$162.19	$162.20	$162.20
Purchase #6	$169.60	6.809%	$181.1481	$181.15	$181.15	$181.10
Purchase #7	$241.27	9.588%	$264.403	$264.40	$264.40	$264.40
7 purchase totals =	$1,069.55		$1,170.7480	$1,170.75	$1,170.75	$1,170.70