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	$187.96	12.143%	$210.784	$210.78	$210.80	$210.80
Purchase #2	$227.25	12.841%	$256.4312	$256.43	$256.45	$256.40
Purchase #3	$68.95	10.381%	$76.1077	$76.11	$76.10	$76.10
Purchase #4	$117.25	11.835%	$131.1265	$131.13	$131.15	$131.10
Purchase #5	$181.67	10.272%	$200.3311	$200.33	$200.35	$200.30
Purchase #6	$26.53	10.861%	$29.4114	$29.41	$29.40	$29.40
Purchase #7	$46.51	11.485%	$51.8517	$51.85	$51.85	$51.90
7 purchase totals =	$856.12		$956.0436	$956.04	$956.10	$956.00