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	$224.50	6.217%	$238.4572	$238.46	$238.45	$238.50
Purchase #2	$154.49	12.870%	$174.3729	$174.37	$174.35	$174.40
Purchase #3	$62.50	6.133%	$66.3331	$66.33	$66.35	$66.30
Purchase #4	$82.89	3.529%	$85.8152	$85.82	$85.80	$85.80
Purchase #5	$103.76	12.104%	$116.3191	$116.32	$116.30	$116.30
Purchase #6	$182.86	4.466%	$191.0265	$191.03	$191.05	$191.00
Purchase #7	$97.50	4.719%	$102.101	$102.10	$102.10	$102.10
7 purchase totals =	$908.50		$974.4250	$974.43	$974.40	$974.40