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	$165.60	8.587%	$179.8201	$179.82	$179.80	$179.80
Purchase #2	$71.50	12.472%	$80.4175	$80.42	$80.40	$80.40
Purchase #3	$250.32	6.806%	$267.3568	$267.36	$267.35	$267.40
Purchase #4	$40.79	5.241%	$42.9278	$42.93	$42.95	$42.90
Purchase #5	$240.71	7.151%	$257.9232	$257.92	$257.90	$257.90
Purchase #6	$37.47	5.817%	$39.6496	$39.65	$39.65	$39.60
Purchase #7	$243.39	7.171%	$260.8435	$260.84	$260.85	$260.80
7 purchase totals =	$1,049.78		$1,128.9385	$1,128.94	$1,128.90	$1,128.80