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	$170.50	11.346%	$189.8449	$189.84	$189.85	$189.80
Purchase #2	$222.46	7.153%	$238.3726	$238.37	$238.35	$238.40
Purchase #3	$142.53	7.265%	$152.8848	$152.88	$152.90	$152.90
Purchase #4	$114.81	11.830%	$128.392	$128.39	$128.40	$128.40
Purchase #5	$25.96	13.247%	$29.3989	$29.40	$29.40	$29.40
Purchase #6	$87.64	5.671%	$92.6101	$92.61	$92.60	$92.60
Purchase #7	$12.41	11.583%	$13.8475	$13.85	$13.85	$13.80
7 purchase totals =	$776.31		$845.3508	$845.34	$845.35	$845.30