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	$50.42	6.489%	$53.6918	$53.69	$53.70	$53.70
Purchase #2	$94.65	11.698%	$105.7222	$105.72	$105.70	$105.70
Purchase #3	$187.59	13.870%	$213.6087	$213.61	$213.60	$213.60
Purchase #4	$96.48	10.756%	$106.8574	$106.86	$106.85	$106.90
Purchase #5	$104.59	4.358%	$109.148	$109.15	$109.15	$109.10
Purchase #6	$175.59	6.202%	$186.4801	$186.48	$186.50	$186.50
Purchase #7	$95.57	10.747%	$105.8409	$105.84	$105.85	$105.80
7 purchase totals =	$804.89		$881.3491	$881.35	$881.35	$881.30