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	$158.53	4.362%	$165.4451	$165.45	$165.45	$165.40
Purchase #2	$153.81	9.243%	$168.0267	$168.03	$168.05	$168.00
Purchase #3	$159.74	6.184%	$169.6183	$169.62	$169.60	$169.60
Purchase #4	$30.52	8.419%	$33.0895	$33.09	$33.10	$33.10
Purchase #5	$114.95	7.776%	$123.8885	$123.89	$123.90	$123.90
Purchase #6	$50.76	8.163%	$54.9035	$54.90	$54.90	$54.90
Purchase #7	$64.70	7.289%	$69.416	$69.42	$69.40	$69.40
7 purchase totals =	$733.01		$784.3876	$784.40	$784.40	$784.30