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	$137.80	5.689%	$145.6394	$145.64	$145.65	$145.60
Purchase #2	$103.62	9.412%	$113.3727	$113.37	$113.35	$113.40
Purchase #3	$97.86	4.629%	$102.3899	$102.39	$102.40	$102.40
Purchase #4	$192.47	13.643%	$218.7287	$218.73	$218.75	$218.70
Purchase #5	$51.26	8.521%	$55.6279	$55.63	$55.65	$55.60
Purchase #6	$37.33	13.799%	$42.4812	$42.48	$42.50	$42.50
Purchase #7	$96.41	9.159%	$105.2402	$105.24	$105.25	$105.20
7 purchase totals =	$716.75		$783.4800	$783.48	$783.55	$783.40