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	$167.56	13.485%	$190.1555	$190.16	$190.15	$190.20
Purchase #2	$123.41	4.320%	$128.7413	$128.74	$128.75	$128.70
Purchase #3	$25.42	9.831%	$27.919	$27.92	$27.90	$27.90
Purchase #4	$236.75	12.236%	$265.7187	$265.72	$265.70	$265.70
Purchase #5	$213.90	5.169%	$224.9565	$224.96	$224.95	$225.00
Purchase #6	$175.41	7.497%	$188.5605	$188.56	$188.55	$188.60
Purchase #7	$45.33	12.325%	$50.9169	$50.92	$50.90	$50.90
7 purchase totals =	$987.78		$1,076.9684	$1,076.98	$1,076.90	$1,077.00