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	$50.79	11.366%	$56.5628	$56.56	$56.55	$56.60
Purchase #2	$99.43	3.700%	$103.1089	$103.11	$103.10	$103.10
Purchase #3	$100.52	10.245%	$110.8183	$110.82	$110.80	$110.80
Purchase #4	$82.95	4.687%	$86.8379	$86.84	$86.85	$86.80
Purchase #5	$40.51	11.479%	$45.1601	$45.16	$45.15	$45.20
Purchase #6	$41.53	3.654%	$43.0475	$43.05	$43.05	$43.00
Purchase #7	$200.88	10.139%	$221.2472	$221.25	$221.25	$221.20
7 purchase totals =	$616.61		$666.7827	$666.79	$666.75	$666.70