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	$13.88	11.511%	$15.4777	$15.48	$15.50	$15.50
Purchase #2	$10.43	8.423%	$11.3085	$11.31	$11.30	$11.30
Purchase #3	$76.25	7.328%	$81.8376	$81.84	$81.85	$81.80
Purchase #4	$157.39	7.115%	$168.5883	$168.59	$168.60	$168.60
Purchase #5	$137.72	11.552%	$153.6294	$153.63	$153.65	$153.60
Purchase #6	$55.96	6.432%	$59.5593	$59.56	$59.55	$59.60
Purchase #7	$98.82	9.410%	$108.119	$108.12	$108.10	$108.10
7 purchase totals =	$550.45		$598.5198	$598.53	$598.55	$598.50