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	$98.98	4.698%	$103.6301	$103.63	$103.65	$103.60
Purchase #2	$243.95	11.346%	$271.6286	$271.63	$271.65	$271.60
Purchase #3	$240.57	10.801%	$266.554	$266.55	$266.55	$266.60
Purchase #4	$142.47	3.522%	$147.4878	$147.49	$147.50	$147.50
Purchase #5	$5.39	5.524%	$5.6877	$5.69	$5.70	$5.70
Purchase #6	$75.87	6.221%	$80.5899	$80.59	$80.60	$80.60
Purchase #7	$38.77	9.513%	$42.4582	$42.46	$42.45	$42.50
7 purchase totals =	$846.00		$918.0363	$918.04	$918.10	$918.10