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	$234.44	13.582%	$266.2816	$266.28	$266.30	$266.30
Purchase #2	$239.98	9.323%	$262.3533	$262.35	$262.35	$262.40
Purchase #3	$160.45	8.370%	$173.8797	$173.88	$173.90	$173.90
Purchase #4	$73.82	6.182%	$78.3836	$78.38	$78.40	$78.40
Purchase #5	$115.82	10.818%	$128.3494	$128.35	$128.35	$128.30
Purchase #6	$194.66	10.853%	$215.7864	$215.79	$215.80	$215.80
Purchase #7	$202.89	9.558%	$222.2822	$222.28	$222.30	$222.30
7 purchase totals =	$1,222.06		$1,347.3162	$1,347.31	$1,347.40	$1,347.40