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	$142.50	11.171%	$158.4187	$158.42	$158.40	$158.40
Purchase #2	$77.50	6.332%	$82.4073	$82.41	$82.40	$82.40
Purchase #3	$224.51	3.675%	$232.7607	$232.76	$232.75	$232.80
Purchase #4	$19.64	4.690%	$20.5611	$20.56	$20.55	$20.60
Purchase #5	$215.58	13.587%	$244.8709	$244.87	$244.85	$244.90
Purchase #6	$28.29	10.569%	$31.28	$31.28	$31.30	$31.30
Purchase #7	$174.98	6.783%	$186.8489	$186.85	$186.85	$186.80
7 purchase totals =	$883.00		$957.1476	$957.15	$957.10	$957.20