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	$206.64	5.411%	$217.8213	$217.82	$217.80	$217.80
Purchase #2	$141.98	13.277%	$160.8307	$160.83	$160.85	$160.80
Purchase #3	$202.76	11.363%	$225.7996	$225.80	$225.80	$225.80
Purchase #4	$20.42	4.527%	$21.3444	$21.34	$21.35	$21.30
Purchase #5	$7.57	12.559%	$8.5207	$8.52	$8.50	$8.50
Purchase #6	$98.67	10.526%	$109.056	$109.06	$109.05	$109.10
Purchase #7	$245.43	8.113%	$265.3417	$265.34	$265.35	$265.30
7 purchase totals =	$923.47		$1,008.7144	$1,008.71	$1,008.70	$1,008.60